Battery and method for manufacturing battery

ABSTRACT

A battery capable of changing its form safely is provided. A bendable battery having a larger thickness is provided. A battery with increased capacity is provided. For an exterior body of the battery, a film in the shape of a periodic wave in one direction is used. A space is provided in an area surrounded by the exterior body and between an end portion of the electrode stack that is not fixed and an interior wall of the exterior body. Furthermore, the phases of waves of a pair of portions of the exterior body between which the electrode stack is located are different from each other. In particular, the phases are different from each other by 180 degrees so that wave crest lines overlap with each other and wave trough lines overlap with each other.

TECHNICAL FIELD

One embodiment of the present invention relates to a battery. Anotherembodiment of the present invention relates to a bendable battery.Another embodiment of the present invention relates to an exterior bodyof a battery.

Note that one embodiment of the present invention is not limited to theabove technical field. Examples of the technical field of one embodimentof the present invention disclosed in this specification and the likeinclude a semiconductor device, a display device, a light-emittingdevice, a power storage device, a memory device, an electronic device, alighting device, an input device, an input/output device, a drivingmethod thereof, and a manufacturing method thereof.

BACKGROUND ART

In recent years, portable information terminals typified by smartphoneshave been actively developed. Portable information terminals, which area kind of electronic devices, are desired to be lightweight and compactfor users. Wearable terminals that are used while being worn on usershave also been developed.

Devices such as wearable devices and portable information terminalsinclude secondary batteries that are capable of being repeatedly chargedand discharged, in many cases. Such devices are required to belightweight and compact and thus there is a problem in that thecapacities of secondary batteries used therein are inevitably low,limiting the operation time of the devices. Secondary batteries used insuch devices should be lightweight and compact and should be capable ofbeing used for a long time.

Patent Document 1 discloses a highly flexible battery using a thin,pliant film-like material as an exterior body.

REFERENCE Patent Document

-   [Patent Document 1] PCT International Publication No. 2012/140709

DISCLOSURE OF INVENTION

However, in the case where a flexible battery is fabricated using thetechnique disclosed in Patent Document 1, bending the battery mightdamage an exterior body thereof unless the thickness of the battery issmall (e.g., 400 μm or smaller). Such a thin battery, however, does nothave enough capacity.

An object of one embodiment of the present invention is to provide abattery that is capable of changing its form safely. Another object isto provide a bendable battery having a larger thickness. Another objectis to provide a battery with increased capacity. Another object is toprovide a highly reliable battery. Another object is to manufacture abattery at low cost.

Note that the description of these objects does not disturb theexistence of other objects. One embodiment of the present invention doesnot necessarily achieve all the objects listed above. Other objects canbe derived from the description of the specification and the like.

One embodiment of the present invention is a battery including a stackand an exterior body. The exterior body has a film-like form and isfolded in half with the stack between facing portions of the exteriorbody. The exterior body includes a pair of first portions, a secondportion, a pair of third portions, and a fourth portion. The pair offirst portions overlaps with each other, and each of the first portionsis surrounded by the second portion, the pair of third portions, and thefourth portion and includes a portion overlapping with the stack. Thesecond portion is a folded portion located between the pair of firstportions. The pair of third portions is belt-like portions locatedopposite to each other with each of the first portions therebetween andextending in a direction intersecting with the second portion. Thefourth portion is a belt-like portion located opposite to the secondportion with each of the first portions therebetween. The exterior bodyis bonded in the third portions and the fourth portion. In an areasurrounded by the exterior body, the stack and the second portion arenot in contact with each other but there is a space between the stackand the second portion.

It is preferred that in a plan view of the exterior body, each of thethird portions in an extension direction thereof be longer than a totallength of one of the first portions, the second portion, and the fourthportion in a direction parallel to the extension direction of the thirdportions.

It is preferred that each of the first portions have a wave shape inwhich a plurality of crest lines and a plurality of trough lines areparallel to each other and alternately located and that each of thethird portions be flat.

It is preferred that each of the first portions include a region inwhich a length of wave period increases and a wave amplitude decreasesas a distance from the second portion decreases.

It is preferred that the pair of first portions of the exterior bodyinclude a region in which the crest lines of one first portion do notoverlap with the trough lines of the other first portion. It isparticularly preferred that the pair of first portions include a regionin which the crest lines thereof overlap with each other and the troughlines thereof overlap with each other.

It is preferred that the second portion not have a wave shape.

It is preferred that one of the crest lines be located between thesecond portion and the trough line of the first portion that is locatedclosest to the second portion.

It is preferred that a distance between an end portion of the stack onthe second portion side and an interior surface of the exterior body inan area surrounded by the exterior body of the battery in the state ofbeing unbent be greater than or equal to π×t when a thickness of thestack is 2t.

Another embodiment of the present invention is a method formanufacturing a battery including a stack in an area surrounded by anexterior body. The method includes the following first to third steps.The first step is to prepare the exterior body in a film form processedto have a wave shape in which a plurality of crest lines and a pluralityof trough lines parallel to each other are alternately located and theplurality of crest lines are located at regular intervals. The secondstep is to fold a part of the exterior body 180° in a directionperpendicular to the crest lines and the trough lines with the stacktherebetween. The third step is to bond another part of the exteriorbody that is band-like, is located outward from the stack, and extendsin a direction perpendicular to the crest lines and the trough lines. Inthe third step, bonding of the exterior body is performed such that apart thereof becomes flat and a distance between the plurality of crestlines increases as a distance from the folded portion of the exteriorbody decreases in a portion of the exterior body overlapping with thestack.

The method preferably includes a fourth step of processing the exteriorbody such that a band-like portion extending in a direction parallel tothe crest lines and the trough lines of the exterior body becomes flat,after the first step and before the second step. It is preferred that inthe second step, the portion of the exterior body that is processed tobe flat be folded.

It is preferred that in the second step, the exterior body be foldedsuch that the crest lines of one of portions of the exterior body thatoverlap with each other do not overlap with the trough lines of theother portion. It is particularly preferred that in the second step, theexterior body be folded such that the crest lines of one of the portionsof the exterior body that overlap with each other overlap with the crestlines of the other portion and the trough lines of the one portionoverlap with the trough lines of the other portion.

According to one embodiment of the present invention, a battery that iscapable of changing its form safely can be provided. Alternatively, abendable battery having a larger thickness can be provided.Alternatively, a battery with increased capacity can be provided.Alternatively, a highly reliable battery can be provided. Alternatively,a battery can be manufactured at low cost.

Note that one embodiment of the present invention does not necessarilyhave all the effects listed above. Other effects can be derived from thedescription of the specification, the drawings, the claims, and thelike.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1E illustrate a structural example of a battery of anembodiment.

FIGS. 2A to 2C are structural examples and a model diagram of a batteryin the state of being bent of an embodiment.

FIGS. 3A and 3B illustrate a method for manufacturing a battery of anembodiment.

FIGS. 4A to 4E illustrate a method for manufacturing a battery of anembodiment.

FIGS. 5A to 5E illustrate a method for manufacturing of a battery of anembodiment.

FIGS. 6A to 6F illustrate a method for manufacturing of a battery of anembodiment.

FIG. 7 illustrates a structural example of a battery of an embodiment.

FIG. 8 illustrates a method for processing a film of an embodiment.

FIGS. 9A to 9C illustrate a method for processing a film of anembodiment.

FIGS. 10A to 10E illustrate a method for manufacturing a battery of anembodiment.

FIG. 11 illustrates a structural example of a battery of an embodiment.

FIGS. 12A to 12E illustrate a structural example of a battery of anembodiment.

FIGS. 13A to 13C illustrate structural examples of batteries ofembodiments.

FIGS. 14A to 14C illustrate structural examples of batteries ofembodiments.

FIGS. 15A to 15C illustrate structural examples of batteries ofembodiments.

FIGS. 16A to 16H illustrate electronic devices of embodiments.

FIGS. 17A to 17C illustrate an electronic device of an embodiment.

FIGS. 18A and 18B illustrate vehicles of embodiments.

FIGS. 19A to 19D are photographs showing the appearances of batteries ofExample 1.

FIGS. 20A and 20B are X-ray images of a battery of Example 1.

FIGS. 21A and 21B are X-ray images of a battery of Example 1.

FIGS. 22A and 22B are X-ray CT images of batteries of Example 1.

FIG. 23 shows the tensile test results of a film of Example 2.

FIGS. 24A and 24B show the measurement results of the amounts ofmoisture entry of Example 3.

FIGS. 25A and 25B illustrate a measurement method of Example 4.

FIG. 26 shows the measurement results of force required to bendbatteries of Example 4.

FIGS. 27A to 27E illustrate a method for fabricating a band of Example5.

FIGS. 28A and 28B are photographs showing a band incorporating a batteryof Example 5.

FIGS. 29A to 29C are photographs showing a band incorporating a batteryof Example 5.

FIGS. 30A to 30C are X-ray images of batteries of Example 6.

FIGS. 31A to 31C are photographs showing the appearances of batteries ofExample 6.

FIG. 32 shows the measurement results of the amounts of moisture entryof Example 6.

FIGS. 33A1 to 33B2 show calculation models of Example 7.

FIGS. 34A and 34B show calculation results of Example 7.

FIGS. 35A and 35B show calculation results of Example 7.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments and examples will be described in detail with reference tothe drawings. Note that the present invention is not limited to thefollowing description. It will be readily appreciated by those skilledin the art that modes and details of the present invention can bemodified in various ways without departing from the spirit and scope ofthe present invention. Thus, the present invention should not beconstrued as being limited to the description in the followingembodiments and examples.

Note that in structures of the present invention described below, thesame portions or portions having similar functions are denoted by thesame reference numerals in different drawings, and the descriptionthereof is not repeated. Note that the same hatching pattern is appliedto portions having similar functions, and the portions are notespecially denoted by reference numerals in some cases.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, the scale of each component is notnecessarily limited to that in the drawings.

Note that in this specification and the like, ordinal numbers such as“first” and “second” are used in order to avoid confusion amongcomponents and do not limit the number.

(Embodiment 1)

In this embodiment, structural examples of batteries of embodiments ofthe present invention and examples of manufacturing methods thereof willbe described.

One embodiment of the present invention is a bendable battery. For anexterior body of the battery, a film in the shape of a periodic wave inone direction is used. The use of the wave shape for the exterior bodyrelieves stress when the exterior body is bent because the form of theexterior body changes such that the period and amplitude of the wave arechanged, preventing the exterior body from being broken.

In an electrode stack included in a battery of one embodiment of thepresent invention, a portion to which a tab or the like is connected isfixed and the relative positions of electrodes are shifted in the otherportion. When the exterior body of the battery is bent, the electrodestack can change its shape with the fixed point used as a support suchthat the relative positions of the electrodes are shifted.

One embodiment of the present invention further includes a space in anarea surrounded by the exterior body and between an end portion of theelectrode stack that is not fixed and an interior wall of the exteriorbody. The space allows the electrode stack to shift when the battery isbent, preventing the portion of the electrode stack and the interiorwall of the exterior body from coming in contact with each other. Oneembodiment of the present invention can prevent the exterior body frombeing broken by the contact between the electrode stack and the exteriorbody accompanying the change in the form of the electrode stack,regardless of the thickness of the electrode stack. For example, even inthe case where the thickness of the battery is larger than 400 μm,larger than or equal to 500 μm, or larger than or equal to 1 mm,changing the form, such as bending, can be safely repeated. It isneedless to say that one embodiment of the present invention can also beused for a very thin battery with a thickness of 1 μm to 400 μminclusive.

There is no limitation on the thickness of the battery as long as it isdetermined in accordance with the capacity required for an electronicdevice provided with the battery, the shape of the device, and the likeso that the thickness is suitable for a use. For example, the thicknessis smaller than or equal to 10 mm, preferably smaller than or equal to 5mm, more preferably smaller than or equal to 4 mm, still more preferablysmaller than or equal to 3 mm.

To form a larger space between the interior wall of the exterior bodyand the electrode stack, the phases of waves of a pair of portions ofthe exterior body between which the electrode stack is sandwiched arepreferably different from each other. Specifically, it is preferred thatwave crest lines of one of the pair of portions between which theelectrode stack is located not overlap with wave trough lines of theother portion. It is particularly preferred that the phases of the wavesof the pair of portions of the exterior body between which the electrodestack is located be different from each other by 180° so that wave crestlines of the pair of portions of the exterior body overlap with eachother and wave trough lines thereof overlap with each other. In thatcase, a space that ensures the largest distance between the electrodestack and the exterior body can be formed. In contrast, it is notpreferred that the phases of the waves of the pair of portions becoordinate so that wave crest lines of one of the portions overlap withwave trough lines of the other portion. In that case, a space is formedto be distorted and the distance between the electrode stack and theexterior body is the shortest.

One embodiment of the present invention can be manufactured, forexample, in such a manner that a film is folded in half in the directionparallel to wave crest lines and wave trough lines with an electrodestack therebetween and bonding is performed by application of pressureand heat such that at least two sides perpendicular to the foldedportion become flat. Furthermore, it is preferred that the film befolded in half such that the phases of waves of opposite portions of thefilm are at least different from each other. It is particularlypreferred that the film be folded such that the phases of the waves aredifferent from each other by 180°.

Here, the phases of the waves of the pair of portions of the exteriorbody between which the electrode stack is sandwiched might be changedafter the bonding. Even in that case, at least a region adjacent to thefolded portion preferably includes a portion in which the phases of thewaves of the pair of portions are different from each other, after thebonding.

The bonding makes the two sides of the film between which the electrodestack is located longer than the natural length of the two sides. Thisgenerates tensile force in the direction perpendicular to wave crestlines and wave trough lines in a portion overlapping with the electrodestack. Meanwhile, reaction in the direction opposite to that of thetensile force occurs in the portion overlapping with the electrode stackso that the wave shape is maintained. The reaction decreases as thedistance from the folded portion decreases; thus, the exterior bodychanges its shape such that the wave thereof is stretched as thedistance from the folded portion decreases. Specifically, the exteriorbody changes its shape such that the length of the wave period increasesand the wave amplitude decreases as the distance from the folded portiondecreases. Through such a mechanism, the bonding is performed such thata bonding portion becomes sufficiently flat, whereby a space can beformed between the folded portion and the electrode stack.

The shape of the wave of the film is important for formation of anenough space between the interior wall of the exterior body and theelectrode stack. A larger space can be formed as the length of the waveperiod of the film decreases and the wave amplitude increases. Forexample, a film in the wave shape with the following length ispreferably used: the length when the film is stretched is 1.02 times ormore, preferably 1.05 times or more, more preferably 1.1 times or more,and twice or less the natural length of the film. Any of a variety ofshapes such as a sine-wave shape, a triangular-wave shape, an arc shape,and a rectangular shape can be used as the wave shape as long as thewave shape has at least repeated crests and troughs in one direction. Alarge wave amplitude might increase the volume of the battery; thus, thelength of the wave period is preferably set small so that the ratio ofthe length of the film when it is stretched to the natural lengththereof is high.

Conditions for the bonding are also important for formation of an enoughspace. Insufficient bonding might result in a wavy shape of the bondingportion instead of a flat shape, failing to form an enough space.Moreover, insufficient bonding might form a gap in the bonding portionwhen the battery changes its form, because the bonding is performed withthe phases of the waves different from each other. However, the use ofan optimized bonding method can avoid such problems. Preferredconditions for the bonding depend on a material of the film, a materialof an adhesive used for the bonding, and the like; for example, in thecase where polypropylene is used for a heat-sealing layer, pressure thatenables planarization of an embossed wave shape is applied at atemperature higher than or equal to the melting point of polypropylene.Furthermore, it is preferred that the bonding be performed by applying ahigh pressure to a portion of the bonding portion in the directionperpendicular to the embossed wave shape (side sealing portion) comparedwith a portion of the bonding portion in the direction parallel to theembossed wave shape (top sealing portion).

Since one embodiment of the present invention allows the shape of asecondary battery to be freely designed, when a secondary battery havinga curved surface is used, for example, the design flexibility of thewhole electronic device is increased, and electronic devices having avariety of designs can be provided. Furthermore, when the secondarybattery is provided along the inner surface of an electronic devicehaving a curved surface, a space in the electronic device can beeffectively used with no waste.

Furthermore, one embodiment of the present invention can increase thecapacity of a secondary battery; accordingly, an electronic device canbe used for a long time with a low frequency of charge.

Thus, an electronic device having a novel structure can be provided.

Specific examples of structures and manufacturing methods will bedescribed below with reference to drawings.

[Structural Example]

FIG. 1A is a plan view of a battery 10 described below as an example.FIG. 1B is a view of the battery 10 seen from the direction shown by ahollow arrow in FIG. 1A. FIGS. 1C, 1D, and 1E are schematiccross-sectional views taken along A1-A2, B1-B2, and C1-C2 in FIG. 1A,respectively.

The battery 10 includes an exterior body 11, a stack 12 located in anarea surrounded by the exterior body 11, and electrodes 13 a and 13 bthat are electrically connected to the stack 12 and extend to theoutside of the exterior body 11. In the area surrounded by the exteriorbody 11, an electrolyte is provided in addition to the stack 12.

The exterior body 11 has a film-like form and is folded in half with thestack 12 between facing portions of the exterior body. The exterior body11 includes a pair of portions 31 between which the stack 12 is located,a folded portion 32, a pair of bonding portions 33, and a bondingportion 34. The pair of bonding portions 33 is belt-like portionsextending in the direction substantially perpendicular to the foldedportion 32 and is located with a portion 31 therebetween. The bondingportion 34 is a belt-like portion located opposite to the folded portion32 with the portion 31 therebetween. The portion 31 can also be referredto as a region surrounded by the folded portion 32, the pair of bondingportions 33, and the bonding portion 34. Here, the electrode 13 a andthe electrode 13 b are partly sandwiched by the bonding portion 34 inFIG. 1A and the like.

At least a surface of the portion 31 of the exterior body 11 has a waveshape in which crests and troughs are repeated in the direction in whichthe pair of bonding portions 33 extends. In other words, the portion 31has a wave shape in which crest lines 21 and trough lines 22 arealternately repeated. In FIG. 1A and the like, crests of the crest lines21 are shown by dashed-dotted lines, and troughs of the trough lines 22are shown by broken lines.

In the plan view, the length of each bonding portion 33 in the extensiondirection is longer than the total length of the bonding portion 34, theportion 31, and the folded portion 32 of the exterior body 11 in thedirection parallel to the extension direction of the bonding portion 33.As illustrated in FIG. 1A, a portion of the folded portion 32 that islocated closest to the bonding portion 34 is closer to the bondingportion 34 by a distance L1 from a line connecting end portions of thepair of bonding portion 33 on the folded portion 32 side.

The stack 12 at least has a structure where positive electrodes andnegative electrodes are alternately stacked. The stack 12 can also becalled an electrode stack. Furthermore, separators may be provided so asto separate the positive electrodes and the negative electrodes. Here,as the number of layers in the stack 12 increases, the capacity of thebattery 10 increases. The details of the stack 12 will be describedbelow.

Here, the thickness of the stack 12 is, for example, larger than orequal to 200 μm and smaller than or equal to 9 mm, preferably largerthan or equal to 400 μm and smaller than or equal to 3 mm, morepreferably larger than or equal to 500 μm and smaller than or equal to 2mm, and is typically approximately 1.5 mm.

As illustrated in FIGS. 1A, 1C, and 1D, in the area surrounded by theexterior body 11, a space (also referred to as a gap or a hollow) 25 isprovided between an end portion of the stack 12 that is closest to thefolded portion 32 and an interior surface of the exterior body 11 thatis located in the folded portion 32. Here, the length of the space 25 inthe direction parallel to the extending direction of the bondingportions 33 is represented by a distance d0. The distance d0 can also bereferred to as the distance between the end portion of the stack 12 thatis closest to the folded portion 32 and the interior surface of theexterior body 11 that is located in the folded portion 32.

The stack 12 is bonded to the electrode 13 a (and the electrode 13 b)extending inside and outside the area surrounded by the exterior body 11through the bonding portion 34. Thus, it can also be said that therelative positions of the stack 12 and the exterior body 11 are fixed bythe bonding portion 34. The electrode 13 a is bonded to the plurality ofpositive electrodes or the plurality of negative electrodes in the stack12, and the electrode 13 b is connected to the plurality of positiveelectrodes or the plurality of negative electrodes to which theelectrode 13 a is not bonded.

Furthermore, as illustrated in FIGS. 1A, 1C, and 1D, it is preferredthat the portion 31 of the exterior body 11 include a region in whichthe length of the wave period increases and the wave amplitude decreasesas the distance from the folded portion 32 decreases. When the battery10 is fabricated to have such a structure, the space 25 can be formed inthe area surrounded by the exterior body 11.

As illustrated in FIGS. 1C and 1D, it is best the pair of portions 31between which the stack 12 is located face each other such that thephases of the waves of the portions 31 are different from each other by180°. In other words, it is preferred that the exterior body 11 befolded with the stack 12 therebetween such that the crest lines 21overlap with each other and the trough lines 22 overlap with each other.In that case, the space 25 with a favorable shape can be provided.

[Space]

Next, the bent form of the battery 10 provided with the space 25 will bedescribed.

FIG. 2A is a simple schematic cross-sectional view of the structure ofthe battery 10 that is partly illustrated.

Here, the pair of portions 31 of the exterior body 11 is distinguishedfrom each other and shown as a portion 31 a and a portion 31 b.Similarly, respective crest lines and respective trough lines of theportion 31 a and the portion 31 b are shown as a crest line 21 a and acrest line 21 b, and a trough line 22 a and a trough line 22 b.

In FIG. 2A, the stack 12 has a structure in which five electrodes 43 arestacked. The electrode 43 corresponds to the electrode 41 or theelectrode 42 in FIG. 1A. The relative positions of the plurality ofelectrodes 43 are fixed at an end portion on the bonding portion 34side. The relative positions of the stack 12 and the exterior body 11are fixed by the bonding portion 34.

In the area surrounded by the exterior body 11, the space 25 is providedin the vicinity of the folded portion 32. Here, the distance between theinterior wall of the exterior body 11 and the end portion of theelectrode 43 on the folded portion 32 side when the exterior body 11 isnot bent is assumed to be the distance d0.

The neutral plane of the battery 10 is referred to as a neutral plane C.Here, the neutral plane C corresponds to the neutral plane of theelectrode 43 that is located in the middle of the five electrodes 43included in the stack 12.

FIG. 2B is a schematic cross-sectional view of the battery 10 in thestate of being bent with a point O at the center to have an arc shape.Here, the battery 10 is bent such that the portion 31 a faces outwardand the portion 31 b faces inward.

As illustrated in FIG. 2B, the portion 31 a that faces outward changesits form such that the wave amplitude becomes smaller and the length ofthe wave period becomes larger. In other words, the distance between thecrest lines 21 a and the distance between the trough lines 22 a of theportion 31 a that faces outward increase. In contrast, the portion 31 bthat faces inward changes its form such that the wave amplitude becomeslarger and the length of the wave period becomes smaller. In otherwords, the distance between the crest lines 21 b and the distancebetween the trough lines 22 b of the portion 31 b that faces inward andis in the state of being bent decrease. In such a manner, the portion 31a and the portion 31 b change their forms, whereby stress applied to theexterior body 11 is relieved, and the battery 10 can be bent without anydamage to the exterior body 11.

As illustrated in FIG. 2B, the stack 12 changes its form such that therelative positions of the plurality of electrodes 43 are shifted. Thisrelieves stress applied to the stack 12, allowing the battery 10 to bebent without any damage to the stack 12. It is assumed in FIG. 2B thatthe electrodes 43 do not stretch due to a bend. When the thickness ofthe electrode 43 is set sufficiently small with respect to the curvatureradius with which the battery 10 is bent, less stress is applied to theelectrodes 43 themselves.

The end portions of the electrodes 43 included in the stack 12 that arelocated outward from the neutral plane C shift to the bonding portion 34side.

In contrast, the end portions of the electrodes 43 located inward fromthe neutral plane C shift to the folded portion 32 side. Here, thedistance between the interior wall of the exterior body 11 and the endportion of the innermost electrode 43 on the folded portion 32 sidedecreases from the distance d0 to a distance d1. Here, the amount ofrelative deviation between the electrode 43 located on the neutral planeC and the innermost electrode 43 is assumed to be a distance d2. Thedistance d1 corresponds to a value obtained by subtracting the distanced2 from the distance d0.

In the case where the distance d0 before bending is smaller than thedistance d2 after bending, the electrodes 43 of the stack 12 that arelocated inward from the neutral plane C come in contact with theinterior wall of the exterior body 11. Thus, a required value of thedistance d0 will be described below.

Description will be given below with reference to FIG. 2C. In FIG. 2C, acurve corresponding to the neutral plane C is shown by a dashed line,and a curve corresponding to the innermost surface of the stack 12 isshown as a curve B by a solid line.

A curve C is the arc of a radius r₀, and a curve B is the arc of aradius r₁. The difference between the radius r₀ and the radius r₁ isassumed to be t. Here, t corresponds to half of the thickness of thestack 12. The arc lengths of the curve C and the curve B are equal toeach other. The central angle of the curve C is assumed to be θ, and thecentral angle of the curve B is assumed to be θ+Δθ.

The distance d2, which is the amount of difference between the edge ofthe curve C and that of the curve B, is calculated from the aboverelation as follows.

$\begin{matrix}\begin{matrix}{{d\; 2} = {r_{1} \times {\Delta\theta}}} \\{= {t \times \theta}}\end{matrix} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

This indicates that the distance d2 can be estimated from the thicknessof the stack 12 and the bending angle and does not depend on the lengthof the stack 12 and the bending curvature radius, for example.

Setting the distance d0 of the space 25 larger than or equal to thedistance d2 as described above can prevent the stack 12 and the exteriorbody 11 from coming in contact with each other when the battery 10 isbent. Thus, in the case where the battery 10 with a thickness of 2t isused while being bent and the maximum angle at which the battery 10 isbent is θ°, the distance d0 between the stack 12 and the interior wallof the exterior body 11 in the space 25 is set to a value greater thanor equal to t×θ.

For example, when the battery is used while being bent at 30°, thedistance d0 of the space 25 is set to a value greater than or equal toπt/6. Similarly, when the battery is used while being bent at 60°, thedistance d0 is set to a value greater than or equal to πt/3; when thebattery is used while being bent at 90°, the distance d0 is set to avalue greater than or equal to πt/2; and when the battery is used whilebeing bent at 180°, the distance d0 is set to a value greater than orequal to πt.

For example, in the case where the battery 10 is not used in the stateof being wound, for example, the maximum bending angle of the battery 10is estimated to be 180°. Thus, when the battery 10 is used in such amanner, the distance d0 is set to a value larger than or equal to πt,preferably larger than πt, whereby the battery 10 can be used for alldevices. The battery 10 can be provided in a variety of electronicdevices in which the battery 10 is used in the state of being bent tohave a V shape or a U shape, for example, the battery 10 is used in thestate of being folded in half.

In the case where the battery 10 is wound so as to circle around acylindrical object once, the distance d0 of the space 25 is set to avalue larger than or equal to 2πt so that the battery 10 can be bent at360°. In the case where the battery 10 is wound so as to circle around acylindrical object more than once, the distance d0 of the space 25 isset to an appropriate value accordingly. In the case where the battery10 is changed in form to have a bellows shape, the distance d0 of thespace 25 is set to an appropriate value depending on the direction, theangle, and the number of bending portions of the battery 10.

The above is the description of the space 25.

[Manufacturing Method Example]

An example of a method for manufacturing the battery 10 will bedescribed below.

First, a flexible film to be the exterior body 11 is prepared.

For the film, a material with high water resistance and high gasresistance is preferably used. As the film used as the exterior body, alayered film in which a metal film and an insulator film are stacked ispreferably used. The metal film can be formed using any of the metalsthat can have the form of a metallic foil, such as aluminum, stainlesssteel, nickel steel, gold, silver, copper, titanium, chromium, iron,tin, tantalum, niobium, molybdenum, zirconium, and zinc, or an alloythereof. As the insulator film, a single-layer film selected from aplastic film made of an organic material, a hybrid material filmcontaining an organic material (e.g., an organic resin or fiber) and aninorganic material (e.g., ceramics), and a carbon-containing inorganicfilm (e.g., a carbon film or a graphite film), or a layered filmincluding two or more of the above films can be used. A metal film iseasy to be embossed. Forming projections by embossing increases thesurface area of the metal film exposed to outside air, achievingefficient heat dissipation.

Then, the flexible film is processed by, for example, embossing to formthe exterior body 11 having a wave shape.

The projections and depressions of the film can be formed by pressing(e.g., embossing). The projections and depressions formed on the film byembossing form an enclosed space whose inner volume is variable, whichis sealed by the film serving as a part of a wall of the sealingstructure. This enclosed space can be said to be formed because the filmhas an accordion structure or a bellows structure. The sealing structureusing the film can prevent entry of water and dust. Note that embossing,which is a kind of pressing, is not necessarily employed and a methodthat allows formation of a relief on part of the film can be employed. Acombination of methods, for example, embossing and any other pressing,may be performed on one film. Alternatively, embossing may be performedon one film more than once.

The projections of the film can have a hollow semicircular shape, ahollow semi-oval shape, a hollow polygonal shape, or a hollow irregularshape. In the case of a hollow polygonal shape, it is preferable thatthe polygon have more than three corners, in which case stressconcentration at the corners can be reduced.

FIG. 3A is an example of a schematic perspective view of the exteriorbody 11 formed in such a manner. The exterior body 11 has a wave shapein which the plurality of crest lines 21 and the plurality of troughlines 22 are alternately arranged on its surface which is the outer sideof the battery 10. Here, the crest lines 21 adjacent to each other andthe trough lines 22 adjacent to each other are preferably arranged atregular intervals.

Subsequently, the exterior body 11 is partly folded such that the stack12 prepared in advance is sandwiched (FIG. 3B). At this time, the lengthof the exterior body 11 is preferably adjusted such that an electrode 13(the electrode 13 a or the electrode 13 b) connected to the stack 12 isexposed to the outside. Furthermore, the width of portions of theexterior body 11 that protrudes beyond the stack 12 is set sufficientlylong in consideration of the thickness of the stack 12 because theprotruding portions serve as the bonding portion 33 and the bondingportion 34 later.

FIG. 3B illustrates an example of the case where the pair of portions 31between which the stack 12 is positioned are located such that thephases of the waves of the portions 31 are different from each other by180°. In other words, FIG. 3B illustrates the case where the exteriorbody 11 is folded such that the crest lines 21 overlap with each otherand the trough lines 22 overlap with each other in the pair of portions31.

Here, the position and the shape of the folded portion 32 of theexterior body 11 will be described. FIG. 4A is a schematiccross-sectional view of the exterior body 11. FIGS. 4B to 4E eachillustrate a cross-sectional shape of the folded portion 32 when thefolding position is a point P1, P2, P3, or P4 in FIG. 4A. Note that thecase where the exterior body 11 is folded in the direction shown by anarrow in FIG. 4A will be described below, and the surface facingdownward corresponds to the outer surface of the battery 10. In FIG. 4A,a portion protruding upward is shown as the trough line 22 and a portionprotruding downward is shown as the crest line 21.

In FIGS. 4B to 4E, a region partly surrounded by the folded portion 32is hatched. Here, a region sandwiched between two positions at which thewave periodicity of the exterior body 11 is lost, as boundaries, is thefolded portion 32. Note that in FIGS. 4B to 4E, the shape of the foldedportion 32 is exaggerated; thus, its perimeter is not shown correctly insome cases.

The point P1 coincides with the trough line 22. As illustrated in FIG.4B, the exterior body 11 is folded at the point P1, whereby the foldedportion 32 can have a substantially arc shape. In addition, folding theexterior body 11 at the point P1 allows the phases of the opposite wavesto be different from each other by 180°.

The point P2 coincides with the crest line 21. As illustrated in FIG.4C, also when the exterior body 11 is folded at the point P2, the foldedportion 32 can have a substantially arc shape. In addition, folding theexterior body 11 at the point P2 allows the phases of the opposite wavesto be different from each other by 180°.

The point P3 is a point located between the crest line 21 and the troughline 22 and closer to the crest line 21 than to the midpoint of thecrest line 21 and the trough line 22. As illustrated in FIG. 4D, thepoint P3 coincides with neither the crest line 21 nor the trough line22, whereby the shape of the folded portion 32 is distorted instead ofbeing vertically symmetrical. In addition, when the exterior body 11 isfolded at the point P3, coincidence of the crest lines, the troughlines, and the crest line and the trough line of the opposite waves canbe avoided.

The point P4 coincides with the midpoint of the crest line 21 and thetrough line 22. As illustrated in FIG. 4E, in the case where theexterior body 11 is folded at the point P4, the shape of the foldedportion 32 is significantly distorted. Specifically, the folded portion32 is more likely to protrude upward or downward. Therefore, it isdifficult to ensure a large distance between the stack 12 and theinterior wall of the exterior body 11 on the side opposite to theprotruding portion.

Here, FIGS. 4B to 4D are the same in that one crest line 21 is locatedbetween the folded portion 32 and the trough line 22 of the portion 31that is closest to the folded portion 32. In particular, FIG. 4Billustrates an example of the case where boundaries of the foldedportion 32 coincide with the crest lines 21 of the waves. The exteriorbody 11 is folded with the crest lines 21 of the two waves or thevicinities thereof regarded as boundaries in this manner, whereby aspace that is large in the thickness direction can be ensured on theinner side of the folded portion 32 and the vicinity thereof. Asdescribed above, it is important to keep a distance between the interiorwall of the exterior body 11 and the outermost electrode of the stackwhen the battery 10 is folded, and the shape illustrated in FIG. 4Ballows the distance to be large.

In contrast, in FIG. 4E, there is no crest line 21 between the foldedportion 32 and the trough line 22 of the portion 31 that is closest tothe folded portion 32, on the lower surface side. Thus, a space that islarge in the thickness direction is unlikely to be formed at the foldedportion 32 and the vicinity thereof.

Here, a portion of the exterior body 11 that is to be the folded portion32 preferably has a flat shape instead of a wave shape. For example, asillustrated in FIG. 5A, the exterior body 11 is partly planarized bybeing sandwiched by molds 51 and 52 each with a flat surface andpressurized or by being pressurized while being heated.

FIG. 5B is a schematic cross-sectional view of the exterior body 11partly planarized in this manner. Here, the exterior body 11 is partlyplanarized such that the crest lines 21 are connected.

FIG. 5C is a schematic cross-sectional view of the exterior body 11folded at a point P5 at the center of the formed flat portion. Asillustrated in FIG. 5C, when the planarized exterior body 11 is used forthe folded portion 32, a space larger than that in FIG. 4B can beformed.

FIGS. 5D and 5E each illustrate an example of the case whereplanarization is performed in a region larger than that in FIG. 5C. Asin FIG. 5B, the exterior body 11 is partly planarized such that thecrest lines 21 are connected. The exterior body 11 is planarized in aregion larger than the thickness of the stack 12 in such a manner,whereby a large space that is uniform in the thickness direction can beformed.

The above is the description of the relation between the position andthe shape of the folded portion.

The exterior body 11 is folded such that the stack 12 is sandwiched, inthe above manner, and then, portions of the exterior body 11 that are tobe the bonding portions 33 are bonded by being pressurized while beingheated.

As illustrated in FIG. 6A, pressure bonding can be performed in such amanner that the exterior body 11 is sandwiched by a pair of molds 53 and54 each with a flat surface. Then, pressure bonding is performed in thedirection perpendicular to the surfaces of the molds 53 and 54, wherebythe portions of the exterior body 11 that are to be the bonding portions33 are bonded so as to be flat as illustrated in FIG. 6B. At this time,clearance is preferably provided to keep a certain distance between themolds 53 and 54. In that case, for example, the following problem can beavoided: the thickness of the bonding portion is reduced by more than acertain value, so that a conductive material (e.g., aluminum foil)contained in the film is exposed, leading to loss or a decrease of theinsulating property.

Pressure bonding is preferably performed at a pressure higher than thatfor subsequent formation of the bonding portion 34, for example, so thatthe bonding portions 33 become sufficiently flat. The pressure dependson a material and the thickness of the exterior body; for example, inthe case where a film with a thickness of approximately 110 μm, thepressure for pressure bonding is higher than or equal to 100 kPa/cm² andlower than or equal to 1000 kPa/cm², and can typically be approximately600 kPa/cm². In addition, in pressure bonding, any temperature isacceptable as long as it is higher than or equal to the melting point ofa material used as a fusing layer; for example, in the case wherepolypropylene is used, the temperature is preferably approximately 175°C.

Furthermore, the thickness of each of the bonding portions 33 afterpressure bonding is preferably smaller than the total thickness of twoexterior bodies 11 before pressure bonding. For example, in the casewhere a layered film including a fusing layer is used as the exteriorbody, the thickness of the fusing layer of the bonding portion 33 afterpressure bonding is preferably 30% or more and 95% or less, morepreferably 50% or more and 90% or less, still more preferably 60% ormore and 80% or less of the total thickness of two fusing layers ofportions of the exterior body 11 that is not subjected to pressurebonding (e.g., the portion 31 and the folded portion 32 of the battery10).

When the bonding portion 33 is formed under the above conditions, evenrepeated changes in the form of the battery 10, such as bends, do notbreak sealing, and leakage of an electrolytic solution and the like withwhich the area surrounded by the exterior body 11 is filled can beprevented. This allows the battery 10 to have extremely high reliabilityand safety. In particular, the bonding portion 33 can be formed in whicha gap is not formed because of a change in the form of the battery 10even in the case where the phases of the waves of facing portions of theexterior body 11 are different from each other by 180° as illustrated inFIG. 6A.

In FIG. 6C, force applied to each portion of the exterior body 11 inbonding is schematically shown by arrows. Here, greater force is shownby longer arrows.

Part of the exterior body 11 having a wave shape before bonding isstretched in the drawing direction (shown by thick arrows) due to itsplanarization by bonding. The stretch generates tensile force to thefolded portion 32 side in the portion 31 of the exterior body 11. Thisforce increases as the distance from the bonding portion 33 decreases,and decreases as the distance from the bonding portion 33 increases.

On the other hand, since the portion 31 has a wave shape, reactionoccurs in the direction opposite to that of the force described above.This reaction increases as the distance from the folded portion 32increases, and decreases as the distance from the folded portion 32decreases.

Application of the above two kinds of force to the portion 31 and thefolded portion 32 stretches the portion 31 such that the wave periodgradually increases as the distance from the folded portion 32decreases, as illustrated in FIG. 6D. The stretch amount increases asthe distance from the bonding portion 33 decreases, and decreases as thedistance from the bonding portion 33 increases; thus, a center portionof the folded portion 32 is depressed to the portion 31 side.

FIGS. 6E and 6F are schematic cross-sectional views before and afterformation of the bonding portions 33. Even in the case where the stack12 is in contact with the interior wall of the exterior body 11 beforebonding as illustrated in FIG. 6E, a stretch of the portion 31 of theexterior body 11 in formation of the bonding portions 33 enables thespace 25 to be formed as illustrated in FIG. 6F.

The bonding portions 33 are formed to be flat in the aforementionedmanner, whereby the space 25 can be formed between the folded portion 32and the stack 12.

Subsequently, an electrolytic solution is introduced from a portion tobe the bonding portion 34. Under reduced pressure or in an inert gasatmosphere, a desired amount of electrolytic solution is dripped intothe area surrounded by the exterior body 11 in the form of a bag.

After that, a portion to be the bonding portion 34 is bonded by a methodsimilar to the above method, so that the bonding portion 34 is formed.In forming the bonding portion 34, an insulating sealing layer may beprovided between the exterior body 11 and the electrodes 13 a and 13 b.The sealing layer melts at the time of pressure bonding, whereby theelectrodes 13 a and 13 b and the film-like exterior body 11 are fixed.

The battery 10 illustrated in FIG. 1A and the like can be manufacturedin the aforementioned manner.

The above is the description of the battery manufacturing methodexample.

[Battery Shape]

As described above, the space 25 can be formed due to a stretch of partof the exterior body 11 in formation of the bonding portions 33. That isto say, the distance d0 between the stack 12 and the exterior body 11 inthe space 25 changes in accordance with the stretch amount of theexterior body 11 in the bonding portion 33. To increase the distance d0,a film with the above ratio of the length of the film with a wave formthat is stretched to the natural length of the film is preferably usedas the exterior body 11.

Furthermore, in the portion 31, as the distance from the bonding portion33 increases, the stretch amount decreases, and thus, the distance d0decreases. In contrast, as the stretch amount of the bonding portion 33increases, tensile force of the portion 31 increases; accordingly, thedistance d0 can be increased even in the position apart from the bondingportion 33. Here, in the case where the same film is used, the stretchamount of the bonding portion 33 increases in proportion to the lengthof the bonding portion 33 in the drawing direction.

FIG. 7 is a schematic top view of the battery 10 with an aspect ratiodifferent from that in FIGS. 1A to 1E. The battery 10 is preferablydesigned such that the ratio of X to Y1 (X/Y1) is higher than or equalto 1, where the length of the bonding portion 33 in the drawingdirection is X and the distance between the pair of bonding portions 33(that is, the width of the portion 31) is Y1. For example, the ratio ofX to Y1 (X/Y1) is higher than or equal to 1.2, higher than or equal to1.5, higher than or equal to 1.7, higher than or equal to 2, or higherthan or equal to 3. Although there is no upper limit on the ratio of Xto Y1, the ratio is preferably, for example, lower than 100 or lowerthan 50 in consideration of productivity.

The ratio of X to Y2 (X/Y2) is preferably, for example, 4/3 or 16/9assuming that the width of the battery 10 including the widths of thebonding portions 33 is Y2, in which case an electronic device providedwith the battery 10 can be easily designed and the battery 10 is morewidely used. In the case where the battery 10 is provided in a narrowobject such as a watch band, the ratio of X to Y2(X/Y2) can be, forexample, higher than or equal to 1.5, higher than or equal to 2, orhigher than or equal to 3.

The above is the description of the battery shape.

[Film Processing Method]

Next, a film processing method that can be used for the exterior body 11will be described.

First, a sheet made of a flexible material is prepared. As the sheet, astacked body, a metal film provided with a heat-seal layer or sandwichedbetween heat-seal layers is used. As the heat-seal layer, a heat-sealresin film containing, e.g., polypropylene or polyethylene is used. Inthis embodiment, a metal sheet, specifically, aluminum foil whose topsurface is provided with a nylon resin and whose bottom surface isprovided with a stack of an acid-proof polypropylene film and apolypropylene film is used as the sheet. The sheet is cut to obtain afilm with a desired size.

Then, the film is embossed, so that the film with unevenness can beobtained. The film includes a plurality of projections and depressions,thereby having a wave pattern that can be visually recognized. Althoughan example where the sheet is cut and then embossing is performed isdescribed here, the order is not particularly limited; embossing may beperformed before cutting the sheet and then the sheet may be cut.Alternatively, the sheet may be cut after thermocompression bonding isperformed with the sheet folded.

Embossing, which is a kind of pressing, will be described below.

FIG. 8 is a cross-sectional view illustrating an example of embossing.Note that embossing refers to processing for forming unevenness on afilm by bringing an embossing roll whose surface has unevenness intocontact with the film with pressure. Note that the embossing roll is aroll whose surface is patterned.

FIG. 8 illustrates an example where both surfaces of a film areembossed, and shows a method for forming a film having projections whosetop portions are on one surface.

FIG. 8 illustrates the state where a film 50 is sandwiched between anembossing roll 55 in contact with the one surface of the film and anembossing roll 56 in contact with the other surface and the film 50 isbeing transferred in a direction 60. The surface of the film ispatterned by pressure or heat. The surface of the film may be patternedby pressure and heat.

The embossing rolls can be formed of metal rolls, ceramic rolls, plasticrolls, rubber rolls, organic resin rolls, lumber rolls, or the like, asappropriate.

In FIG. 8, embossing is performed using the male embossing roll 56 andthe female embossing roll 55. The male embossing roll 56 has a pluralityof projections 56 a. The projections correspond to projections formed ona film to be processed. The female embossing roll 55 has a plurality ofprojections 55 a. Between adjacent projections 55 a, a depression ispositioned into which a projection formed on the film by the projection56 a of the male embossing roll 56 fits.

Successive embossing by which the film 50 partly stands out anddebossing by which the film 50 is partly indented can form a projectionand a flat portion successively. In this manner, a pattern can be formedon the film 50.

Next, a method for forming a film having a plurality of projections,which is a method different from that described with reference to FIG.8, will be described with reference to FIGS. 9A to 9C. FIGS. 9A to 9Cillustrate an example where one surface of a film is embossed, and showa method for forming a film having projections whose top portions are onone surface.

FIG. 9A illustrates the state where the film 50 is sandwiched betweenthe embossing roll 55 in contact with one surface of the film and a roll57 in contact with the other surface and the film 50 is beingtransferred in the direction 60. Note that a roll 57 may be fixedwithout rotating. Since the embossing roll 55 is provided only on onesurface of the film here, a plurality of projections formed on the filmhave no space. This means that the film has protrusions on one surfaceand is flat on the other surface.

Then, as illustrated in FIG. 9B, a film 61 in which projections areformed on one surface by embossing is partly removed. Here, the film ispartly removed from a flat surface, that is, the surface that was incontact with the roll 57, of the projections. As a method for removingpart of the film, thermal removal by laser irradiation, chemical removalby dropping an etchant, physical removal using a tool, or the like canbe given.

As a result, spaces 64 can be formed in the projections 63 asillustrated in FIG. 9C. In this manner, a film 62 having the projections63 can be formed.

Note that in the method of forming a film illustrated in FIGS. 9A to 9C,a metal film is preferably used as the film 50. In addition, a heat-seallayer is preferably provided on one or both surfaces of the metal filmafter the process illustrated in FIGS. 9A to 9C.

Since processing is performed using the embossing rolls in theaforementioned manner, a processing apparatus can be small. Furthermore,a film before being cut can be processed, achieving excellentproductivity. Note that a method for processing a film is not limited toprocessing using embossing rolls; a film can be processed by pressing apair of embossing plates having a surface with unevenness against thefilm. In that case, one of the embossing plates may be flat and the filmmay be processed in a plurality of steps.

[Secondary Battery Manufacturing Method Example]

An example of a manufacturing method particularly when a secondarybattery is used as the battery 10 will be described below. Note that thedescription of points already described above is omitted in some cases.

Here, the film-like exterior body 11 having a wave shape is folded inhalf so that two end portions overlap with each other, and three sidesare sealed using an adhesive layer.

The exterior body 11 composed of a film processed to have a wave shapeis folded so that a state illustrated in FIG. 10A is obtained.

Then, as illustrated in FIG. 10B, a stack including a positive electrodecurrent collector 72, a separator 73, and a negative electrode currentcollector 74 included in a secondary battery is prepared. Although notillustrated in the drawings, a positive electrode active material layeris formed on part of a surface of the positive electrode currentcollector 72, whereas a negative electrode active material layer isformed on part of a surface of the negative electrode current collector74. The positive electrode current collector 72 and the negativeelectrode current collector 74 can each be formed using a highlyconductive material that is not alloyed with a carrier ion such as alithium ion, for example, a metal such as stainless steel, gold,platinum, zinc, iron, nickel, copper, aluminum, titanium, or tantalum oran alloy thereof. Alternatively, an aluminum alloy to which an elementwhich improves heat resistance, such as silicon, titanium, neodymium,scandium, or molybdenum, is added can be used. Still alternatively, ametal element which forms silicide by reacting with silicon can be used.Examples of the metal element which forms silicide by reacting withsilicon include zirconium, titanium, hafnium, vanadium, niobium,tantalum, chromium, molybdenum, tungsten, cobalt, nickel, and the like.The current collectors can each have a foil-like shape, a plate-likeshape (sheet-like shape), a net-like shape, a cylindrical shape, a coilshape, a punching-metal shape, an expanded-metal shape, or the like asappropriate. The current collectors each preferably have a thickness of5 μm to 40 μm inclusive. Note that in the example illustrated here, forsimplicity, one stack including the positive electrode current collector72 provided with the positive electrode active material layer, theseparator 73, and the negative electrode current collector 74 providedwith the negative electrode active material layer is packed in anexterior body. To increase the capacity of a secondary battery, aplurality of the stacks are stacked and packed in an exterior body.

In addition, two lead electrodes 76 with sealing layers 75 illustratedin FIG. 10C are prepared. Each of the lead electrodes 76 is alsoreferred to as a lead terminal or a tab and is provided in order to leada positive electrode or a negative electrode of a secondary battery tothe outside of an exterior film. Aluminum and nickel-plated copper areused for the positive electrode lead and the negative electrode lead,respectively.

Then, the positive electrode lead is electrically connected to aprotruding portion of the positive electrode current collector 72 byultrasonic welding or the like, and the negative electrode lead iselectrically connected to a protruding portion of the negative electrodecurrent collector 74 by ultrasonic welding or the like.

Then, two sides of the film-like exterior body 11 are sealed bythermocompression bonding by the above-described method, and one side isleft open for introduction of an electrolytic solution. In this manner,the bonding portions 33 are formed. After that, under reduced pressureor in an inert gas atmosphere, a desired amount of electrolytic solutionis dripped into the film-like exterior body 11 in the form of a bag.Lastly, the side of the film which has been left open without beingsubjected to thermocompression bonding is sealed by thermocompressionbonding, so that the bonding portion 34 is formed. In thermocompressionbonding, the sealing layers 75 provided on the lead electrodes are alsomelted, thereby fixing the lead electrodes and the film-like exteriorbody 11 to each other.

In this manner, the battery 10 illustrated in FIG. 10D, which is asecondary battery, can be manufactured.

The exterior body 11 in the form of a film of the battery 10, which isthe obtained secondary battery, has a pattern of waves. A region betweenthe edge and a dotted line in FIG. 10D is the bonding portions 33 andthe bonding portion 34, and the region is processed to be flat.

FIG. 10E illustrates an example of a cross section taken alongdashed-dotted line D1-D2 in FIG. 10D.

As illustrated in FIG. 10E, the positive electrode current collector 72,a positive electrode active material layer 78, the separator 73, anegative electrode active material layer 79, and the negative electrodecurrent collector 74 are stacked in this order and surrounded by thefolded film-like exterior body 11. The folded film-like exterior body 11is sealed by the bonding portion 34 in end portions of the film-likeexterior body 11 and a space sandwiched by the film-like exterior body11 is provided with an electrolytic solution 77. In other words, thespace surrounded by the film-like exterior body 11 is filled with theelectrolytic solution 77.

Examples of positive electrode active materials that can be used for thepositive electrode active material layer 78 include a composite oxidewith an olivine crystal structure, a composite oxide with a layeredrock-salt crystal structure, and a composite oxide with a spinel crystalstructure. For example, a compound such as LiFeO₂, LiCoO₂, LiNiO₂,LiMn₂O₄, V₂O₅, Cr₂O₅, or MnO₂ is used.

Alternatively, a complex material (LiMPO₄ (general formula) (M is one ormore of Fe(II), Mn(II), Co(II), and Ni(II))) can be used. Typicalexamples of the general formula LiMPO₄ which can be used as a materialare lithium compounds such as LiFePO₄, LiNiPO₄, LiCoPO₄, LiMnPO₄,LiFe_(a)Ni_(b)PO₄, LiFe_(a)Co_(b)PO₄, LiFe_(a)Mn_(b)PO₄,LiNi_(a)Co_(b)PO₄, LiNi_(a)Mn_(b)PO₄ (a+b≤1, 0<a<1, and 0<b<1),LiFe_(c)Ni_(d)Co_(e)PO₄, LiFe_(c)Ni_(d)Mn_(e)PO₄,LiNi_(c)Co_(d)Mn_(e)PO₄ (c+d+e≤1, 0<c<1, 0<d<1, and 0<e<1), andLiFe_(f)Ni_(g)Co_(h)Mn_(i)PO₄ (f+g+h+i≤1, 0<f<1, 0<g<1, 0<h<1, and0<i<1).

Alternatively, a complex material such as Li_((2-j))MSiO₄ (generalformula) (M is one or more of Fe(II), Mn(II), Co(II), and Ni(II); 0≤j≤2)may be used. Typical examples of the general formula Li_((2-j))MSiO₄which can be used as a material are lithium compounds such asLi_((2-j))FeSiO₄, Li_((2-j))NiSiO₄, Li_((2-j))CoSiO₄, Li_((2-j))MnSiO₄,Li_((2-j))Fe_(k)Ni_(l)SiO₄, Li_((2-j))Fe_(k)Co_(l)SiO₄,Li_((2-j))Fe_(k)Mn_(l)SiO₄, Li_((2-j))Ni_(k)Co_(l)SiO₄,Li_((2-j))Ni_(k)Mn_(l)SiO₄ (k+l≤1, 0<k<1, and 0<l<1),Li_((2-j))Fe_(m)Ni_(n)Co_(q)SiO₄, Li_((2-j))Fe_(m)Ni_(n)Mn_(q)SiO₄,Li_((2-j))Ni_(m)Co_(n)Mn_(q)SiO₄ (m+n+q≤1, 0<m<1, 0<n<1, and 0<q<1), andLi_((2-j))Fe_(r)Ni_(s)Co_(t)Mn_(u)SiO₄ (r+s+t+u≤1, 0<r<1, 0<s<1, 0<t<1,and 0<u<1).

Still alternatively, a nasicon compound expressed by A_(x)M₂(XO₄)₃(general formula) (A =Li, Na, or Mg, M=Fe, Mn, Ti, V, Nb, or Al, X=S, P,Mo, W, As, or Si) can be used for the positive electrode activematerial. Examples of the nasicon compound are Fe₂(MnO₄)₃, Fe₂(SO₄)₃,and Li₃Fe₂(PO₄)₃. Further alternatively, a compound expressed byLi₂MPO₄F, Li₂MP₂O₇, or Li₅MO₄ (general formula) (M=Fe or Mn), aperovskite fluoride such as NaFeF₃ and FeF₃, a metal chalcogenide (asulfide, a selenide, or a telluride) such as TiS₂ and MoS₂, an oxidewith an inverse spinel structure such as LiMVO₄, a vanadium oxide (V₂O₅,V₆O₁₃, LiV₃O₈, or the like), a manganese oxide, an organic sulfurcompound, or the like can be used as the positive electrode activematerial.

In the case where carrier ions are alkali metal ions other than lithiumions, or alkaline-earth metal ions, a material containing an alkalimetal (e.g., sodium and potassium) or an alkaline-earth metal (e.g.,calcium, strontium, barium, beryllium, and magnesium) instead of lithiummay be used as the positive electrode active material.

As the separator 73, an insulator such as cellulose (paper),polypropylene with pores, or polyethylene with pores can be used.

As an electrolyte of the electrolytic solution 77, a material that hascarrier ion mobility and contains lithium ions as carrier ions is used.Typical examples of the electrolyte are lithium salts such as LiPF₆,LiClO₄, LiAsF₆, LiBF₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, and Li(C₂F₅SO₂)₂N. One ofthese electrolytes may be used alone, or two or more of them may be usedin an appropriate combination and in an appropriate ratio.

As a solvent of the electrolytic solution, a material with carrier ionmobility is used. As the solvent of the electrolytic solution, anaprotic organic solvent is preferably used. Typical examples of aproticorganic solvents include ethylene carbonate (EC), propylene carbonate,dimethyl carbonate, diethyl carbonate (DEC), γ-butyrolactone,acetonitrile, dimethoxyethane, tetrahydrofuran, and the like, and one ormore of these materials can be used. When a gelled high-molecularmaterial is used as the solvent of the electrolytic solution, safetyagainst liquid leakage and the like is improved. Furthermore, thestorage battery can be thinner and more lightweight. Typical examples ofgelled high-molecular materials include a silicone gel, an acrylic gel,an acrylonitrile gel, a polyethylene oxide-based gel, a polypropyleneoxide-based gel, a fluorine-based polymer gel, and the like.Alternatively, the use of one or more kinds of ionic liquids (roomtemperature molten salts) which have features of non-flammability andnon-volatility as a solvent of the electrolytic solution can prevent thestorage battery from exploding or catching fire even when the storagebattery internally shorts out or the internal temperature increasesowing to overcharging and others. An ionic liquid is a salt in the fluidstate and has high ion mobility (conductivity). An ionic liquid containsa cation and an anion. Examples of ionic liquids include an ionic liquidcontaining an ethylmethylimidazolium (EMI) cation and an ionic liquidcontaining an N-methyl-N-propylpiperidinium (PP₁₃) cation.

Instead of the electrolytic solution, a solid electrolyte including aninorganic material such as a sulfide-based inorganic material or anoxide-based inorganic material, or a solid electrolyte including amacromolecular material such as a polyethylene oxide (PEO)-basedmacromolecular material may alternatively be used. When the solidelectrolyte is used, a separator and a spacer are not necessary.Furthermore, the battery can be entirely solidified; therefore, there isno possibility of liquid leakage and thus the safety of the battery isdramatically increased.

A material with which lithium can be dissolved and precipitated or amaterial into and from which lithium ions can be inserted and extractedcan be used for a negative electrode active material used in thenegative electrode active material layer 79; for example, metal lithium,a carbon-based material, an alloy-based material, or the like can beused.

The metal lithium is preferable because of its low redox potential(3.045 V lower than that of a standard hydrogen electrode) and highspecific capacity per unit weight and per unit volume (3860 mAh/g and2062 mAh/cm³).

Examples of the carbon-based material include graphite, graphitizingcarbon (soft carbon), non-graphitizing carbon (hard carbon), a carbonnanotube, graphene, fullerene, carbon black, and the like.

Examples of the graphite include artificial graphite such as meso-carbonmicrobeads (MCMB), coke-based artificial graphite, or pitch-basedartificial graphite and natural graphite such as spherical naturalgraphite.

Graphite has a low potential substantially equal to that of metallithium (higher than or equal to 0.1 V and lower than or equal to 0.3 Vvs. Li/Li⁺) when lithium ions are intercalated into the graphite (whilea lithium-graphite intercalation compound is formed). For this reason, alithium-ion secondary battery can have a high operating voltage. Inaddition, graphite is preferable because of its advantages such asrelatively high capacity per unit volume, small volume expansion, lowcost, and safety greater than that of metal lithium.

For the negative electrode active material, an alloy-based material oran oxide which enables charge-discharge reactions by an alloyingreaction and a dealloying reaction with lithium can be used. In the casewhere carrier ions are lithium ions, a material containing at least oneof Al, Si, Ge, Sn, Pb, Sb, Bi, Ag, Au, Zn, Cd, In, Ga, and the like canbe used as the alloy-based material, for example. Such elements havehigher capacity than carbon. In particular, silicon has a significantlyhigh theoretical capacity of 4200 mAh/g. For this reason, silicon ispreferably used as the negative electrode active material. Examples ofthe alloy-based material that uses such an element include Mg₂Si, Mg₂Ge,Mg₂Sn, SnS₂, V₂Sn₃, FeSn₂, CoSn₂, Ni₃Sn₂, Cu₆Sn₅, Ag₃Sn, Ag₃Sb, Ni₂MnSb,CeSb₃, LaSn₃, La₃Co₂Sn₇, CoSb₃, InSb, SbSn, and the like.

Alternatively, for the negative electrode active material, SiO, SnO,SnO₂, or an oxide such as titanium dioxide (TiO₂), lithium titaniumoxide (Li₄Ti₅O₁₂), a lithium-graphite intercalation compound (Li_(x)C₆),niobium pentoxide (Nb₂O₅), tungsten oxide (WO₂), or molybdenum oxide(MoO₂) can be used. Note that SiO refers to the powder of a siliconoxide including a silicon-rich portion and can also be referred to asSiO_(y) (2>y>0). Examples of SiO include a material containing one ormore of Si₂O₃, Si₃O₄, and Si₂O and a mixture of Si powder and silicondioxide (SiO₂). Furthermore, SiO may contain another element (e.g.,carbon, nitrogen, iron, aluminum, copper, titanium, calcium, andmanganese). In other words, SiO refers to a material containing two ormore of single crystal silicon, amorphous silicon, polycrystal silicon,Si₂O₃, Si₃O₄, Si₂O, and SiO₂. Furthermore, SiO is a colored material.Thus, SiO can be distinguished from SiO_(x) (x is 2 or more), which isclear and colorless or white. Note that in the case where a secondarybattery is fabricated using SiO as a material thereof and the SiO isoxidized because of repeated charge and discharge cycles, SiO is changedinto SiO₂ in some cases.

Still alternatively, for the negative electrode active materials,Li_(3-x)M_(x)N (M=Co, Ni, or Cu) with a Li₃N structure, which is anitride containing lithium and a transition metal, can be used. Forexample, Li_(2.6)Co_(0.4)N₃ is preferable because of high charge anddischarge capacity (900 mAh/g and 1890 mAh/cm³).

A nitride containing lithium and a transition metal is preferably used,in which case lithium ions are contained in the negative electrodeactive materials and thus the negative electrode active materials can beused in combination with a material for a positive electrode activematerial which does not contain lithium ions, such as V₂O₅ or Cr₃O₈. Inthe case of using a material containing lithium ions as a positiveelectrode active material, the nitride containing lithium and atransition metal can be used for the negative electrode active materialby extracting the lithium ions contained in the positive electrodeactive material in advance.

Alternatively, a material which causes a conversion reaction can be usedfor the negative electrode active materials; for example, a transitionmetal oxide which does not cause an alloy reaction with lithium, such ascobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may beused. Other examples of the material which causes a conversion reactioninclude oxides such as Fe₂O₃, CuO, Cu₂O, RuO₂, and Cr₂O₃, sulfides suchas CoS_(0.89), NiS, and CuS, nitrides such as Zn₃N₂, Cu₃N, and Ge₃N₄,phosphides such as NiP₂, FeP₂, and CoP₃, and fluorides such as FeF₃ andBiF₃. Note that any of the fluorides can be used as a positive electrodeactive material because of its high potential.

The negative electrode active material layer 79 may further include abinder for increasing adhesion of active materials, a conductiveadditive for increasing the conductivity of the negative electrodeactive material layer, and the like in addition to the above negativeelectrode active materials.

In the secondary battery, for example, the separator 73 has a thicknessof approximately 15 μm to 30 μm, the positive electrode currentcollector 72 has a thickness of approximately 10 μm to 40 μm, thepositive electrode active material layer 78 has a thickness ofapproximately 50 μm to 100 μm, the negative electrode active materiallayer 79 has a thickness of approximately 50 μm to 100 μm, and thenegative electrode current collector 74 has a thickness of approximately5 μm to 40 μm. The film-like exterior body 11 has a thickness ofapproximately 20 μm to 500 μm. The height of each of the projections ofthe film-like exterior body 11 is approximately 5 μm to 400 μm. If theheight of each of the projections of the film-like exterior body 11 is 2mm or more, the total thickness of the secondary battery becomes toolarge.

The battery capacity per unit volume is preferably as large as possible.The battery capacity per unit volume becomes large as the proportion ofthe volume of a battery portion to the total volume of the secondarybattery increases. When the heights of the projections of the film-likeexterior body 11 are made large, the total thickness of the secondarybattery is increased and the proportion of the volume of the batteryportion to the total volume is decreased, resulting in a small batterycapacity.

Note that the adhesive layer is formed in the following manner: a layermade of polypropylene is provided on the surface of the film on the sidewhere the film is attached, and only a thermocompression-bonded portionbecomes the adhesive layer.

FIG. 10E illustrates an example where the bottom side of the film-likeexterior body 11 is fixed and pressure bonding is performed. In thiscase, the top side is greatly bent and a step is formed. Thus, when aplurality of the above-described stacks (e.g., eight or more stacks) areprovided between facing portions of the folded film-like exterior body11, the step is large and stress applied to the top side of thefilm-like exterior body 11 might be too high. Furthermore, the edge ofthe top side of the film might be misaligned with the edge of the bottomside of the film. To prevent misalignment of the edges, a step may beprovided on the bottom side of the film and pressure bonding may beperformed at a center portion so that stress is uniformly applied.

In the case where the misalignment is large, there is a region wherepart of the edge of one film does not overlap with the other film. Tocorrect the misalignment of the edges of the top and bottom sides of thefilm, such a region may be cut off

Here, a current flow in charging a secondary battery will be describedwith reference to FIG. 11. When a secondary battery using lithium isregarded as a closed circuit, lithium ions transfer and a current flowsin the same direction. Note that in the secondary battery using lithium,an anode and a cathode change places in charge and discharge, and anoxidation reaction and a reduction reaction occur on the correspondingsides; hence, an electrode with a high redox potential is called apositive electrode and an electrode with a low redox potential is calleda negative electrode. For this reason, in this specification, thepositive electrode is referred to as a “positive electrode” and thenegative electrode is referred to as a “negative electrode” in all thecases where charge is performed, discharge is performed, a reverse pulsecurrent is supplied, and a charging current is supplied. The use of theterms “anode” and “cathode” related to an oxidation reaction and areduction reaction might cause confusion because the anode and thecathode change places at the time of charging and discharging. Thus, theterms “anode” and “cathode” are not used in this specification. If theterm “anode” or “cathode” is used, it should be mentioned that the anodeor the cathode is which of the one at the time of charging or the one atthe time of discharging and corresponds to which of a positive electrodeor a negative electrode.

Two terminals in FIG. 11 are connected to a charger, and the battery 10is charged. As the charge of the battery 10 proceeds, a potentialdifference between electrodes increases. In FIG. 11, electrons flow froma terminal outside the battery 10 to the positive electrode currentcollector 72, and a current flows from the positive electrode currentcollector 72 to the negative electrode current collector 74 in thebattery 10. In FIG. 11, the direction of the current flow from thenegative electrode to the terminal outside the battery 10 is regarded asthe positive direction. In other words, the direction in which acharging current flows is regarded as the direction of a current.

[Example of Electrode Stack]

A structural example of a stack including a plurality of electrodes willbe described below.

FIG. 12A is a top view of the positive electrode current collector 72.FIG. 12B is a top view of the separator 73. FIG. 12C is a top view ofthe negative electrode current collector 74. FIG. 12D is a top view ofthe sealing layer 75 and the lead electrode 76. FIG. 12E is a top viewof the film-like exterior body 11.

The dimensions of the components are substantially the same in FIGS. 12Ato 12E. A region 71 surrounded by a dashed-dotted line in FIG. 12E hassubstantially the same dimension as the separator in FIG. 12B. A regionbetween the edge and a dashed line in FIG. 12E corresponds to thebonding portions 33 and the bonding portion 34.

FIG. 13A illustrates an example where the positive electrode activematerial layer 78 is provided on both surfaces of the positive electrodecurrent collector 72. Specifically, the negative electrode currentcollector 74, the negative electrode active material layer 79, theseparator 73, the positive electrode active material layer 78, thepositive electrode current collector 72, another positive electrodeactive material layer 78, another separator 73, another negativeelectrode active material layer 79, and another negative electrodecurrent collector 74 are stacked in this order. FIG. 13B is across-sectional view of the layered structure taken along a plane 80.

Note that although FIG. 13A illustrates an example where two separatorsare used, the following structure may be employed: one separator isfolded and two end portions are sealed to form a bag form, and thepositive electrode current collector 72 is provided in the bag form. Thepositive electrode active material layer 78 is formed on both surfacesof the positive electrode current collector 72 provided in the bag-likeseparator.

The negative electrode active material layer 79 may be provided on bothsurfaces of the negative electrode current collector 74. In a secondarybattery illustrated in FIG. 13C, three negative electrode currentcollectors 74 each provided with the negative electrode active materiallayers 79 on both surfaces, four positive electrode current collectors72 each provided with the positive electrode active material layers 78on both surfaces, and eight separators 73 are sandwiched between twonegative electrode current collectors 74 each having the negativeelectrode active material layer 79 on one surface. In this case, fourbag-like separators can be used instead of eight separators.

The capacity of the secondary battery can be increased by increasing thenumber of the stacks. In addition, when the positive electrode activematerial layers 78 are provided on both surfaces of the positiveelectrode current collector 72 and the negative electrode activematerial layers 79 are provided on both surfaces of the negativeelectrode current collector 74, the thickness of the secondary batterycan be made small.

FIG. 14A illustrates a secondary battery in which the positive electrodeactive material layer 78 is provided on one surface of the positiveelectrode current collector 72 and the negative electrode activematerial layer 79 is provided on one surface of the negative electrodecurrent collector 74. Specifically, the negative electrode activematerial layer 79 is provided on one surface of the negative electrodecurrent collector 74 and the separator 73 is stacked in contact with thenegative electrode active material layer 79. The positive electrodeactive material layer 78 that is provided on one surface of the positiveelectrode current collector 72 is in contact with a surface of theseparator 73 remote from the negative electrode active material layer79. Another positive electrode current collector 72 whose one surface isprovided with the positive electrode active material layer 78 is incontact with the other surface of the positive electrode currentcollector 72. Note that the positive electrode current collectors 72 areprovided such that the surfaces remote from the positive electrodeactive material layers 78 face each other. Another separator 73 isstacked thereon, and another negative electrode active material layer 79provided on one surface of another negative electrode current collector74 is stacked in contact with the separator. FIG. 14B is across-sectional view of the layered structure in FIG. 14A, which istaken along a plane 90.

Although two separators are used in FIG. 14A, the following structuremay be employed: one separator is folded and two end portions are sealedto form a bag form, and two positive electrode current collectors 72each provided with the positive electrode active material layer 78 onone surface are provided in the bag form.

In FIG. 14C, a plurality of the stacks illustrated in FIG. 14A arestacked. In FIG. 14C, the negative electrode current collectors 74 areprovided such that the surfaces remote from the negative electrodeactive material layers 79 face each other. In FIG. 14C, twelve positiveelectrode current collectors 72, twelve negative electrode currentcollectors 74, and twelve separators 73 are stacked.

A secondary battery with a structure in which the positive electrodeactive material layer 78 is provided on one surface of the positiveelectrode current collector 72 and the negative electrode activematerial layer 79 is provided on one surface of the negative electrodecurrent collector 74, is thicker than a secondary battery with astructure in which the positive electrode active material layers 78 areprovided on both surfaces of the positive electrode current collector 72and the negative electrode active material layers 79 are provided onboth surfaces of the negative electrode current collector 74. However,the surface of the positive electrode current collector 72 on which thepositive electrode active material layer 78 is not provided faces thesurface of another positive electrode current collector 72 on which thepositive electrode active material layer 78 is not provided; as aresult, metals are in contact with each other. Similarly, the surface ofthe negative electrode current collector 74 on which the negativeelectrode active material layer 79 is not provided faces the surface ofanother negative electrode current collector 74 on which the negativeelectrode active material layer 79 is not provided; as a result, metalsare in contact with each other. Surfaces where the metals are in contactwith each other easily slide on each other owing to the low friction.Since the metals in the secondary battery slide on each other at thetime of bending, the secondary battery is easily bent.

The protruding portions of the positive electrode current collector 72and the negative electrode current collector 74 are also referred to astab portions. The tab portions of the positive electrode currentcollector 72 and the negative electrode current collector 74 are easilycut when the secondary battery is bent. This is because the tab portionsare long and narrow protrusions and the stress is likely to be appliedto the roots of the tab portions.

In the structure in which the positive electrode active material layer78 is provided on one surface of the positive electrode currentcollector 72 and the negative electrode active material layer 79 isprovided on one surface of the negative electrode current collector 74,there are a surface where the positive electrode current collectors 72are in contact with each other and a surface where the negativeelectrode current collectors 74 are in contact with each other. Thesurface where the current collectors are in contact with each other haslow friction resistance and thus easily reduces the stress due to thedifference in radius of curvature that occurs when the battery ischanged in form. Furthermore, the total thickness of each tab portion islarge in the structure in which the positive electrode active materiallayer 78 is provided on one surface of the positive electrode currentcollector 72 and the negative electrode active material layer 79 isprovided on one surface of the negative electrode current collector 74;thus, the stress is distributed as compared with the case of thestructure in which the positive electrode active material layers 78 areprovided on both surfaces of the positive electrode current collector 72and the negative electrode active material layers 79 are provided onboth surfaces of the negative electrode current collector 74. As aresult, the tab portion is less likely to be cut.

In the case of thus stacking layers, ultrasonic welding is performed tofix and electrically connect all the positive electrode currentcollectors 72 at a time. Furthermore, when ultrasonic welding isperformed with the positive electrode current collectors 72 overlappingwith a lead electrode, they can be electrically connected efficiently.

Ultrasonic welding can be performed in such a manner that ultrasonicwaves are applied to the tab portion of the positive electrode currentcollector placed so as to overlap with a tab portion of another positiveelectrode current collector, while pressure is applied thereto.

The separators 73 preferably have a shape that helps prevent anelectrical short circuit between the positive electrode currentcollector 72 and the negative electrode current collector 74. Forexample, the width of each of the separators 73 is preferably largerthan those of the positive electrode current collector 72 and thenegative electrode current collector 74 as illustrated in FIG. 15A, inwhich case the positive electrode current collector 72 and the negativeelectrode current collector 74 are less likely to come in contact witheach other even when the relative positions of the positive electrodecurrent collector 72 and the negative electrode current collector 74 areshifted because of a change in form, such as a bend. Alternatively, asillustrated in FIG. 15B, one separator 73 is preferably folded into abellows shape, or as illustrated in FIG. 15C, one separator 73 ispreferably wrapped around the positive electrode current collectors 72and the negative electrode current collectors 74 alternately. In thosecases, the positive electrode current collector 72 and the negativeelectrode current collector 74 do not come in contact with each othereven when the relative positions of the positive electrode currentcollector 72 and the negative electrode current collector 74 areshifted. In FIGS. 15B and 15C, the separator 73 is provided so as topartly cover a side surface of a layered structure of the positiveelectrode current collectors 72 and the negative electrode currentcollectors 74.

Although FIGS. 15A to 15C do not illustrate the positive electrodeactive material layer 78 and the negative electrode active materiallayer 79, the above description can be referred to for forming methodsthereof. Although an example where the positive electrode currentcollectors 72 and the negative electrode current collectors 74 arealternately arranged is described here, two positive electrode currentcollectors 72 or two negative electrode current collectors 74 may beadjacent to each other as described above.

In an example in this embodiment, one rectangle film is folded in halfand two end portions are made to overlap with each other for sealing.However, the shape of the film is not limited to a rectangle and can bea polygon such as a triangle, a square, or a pentagon or any symmetricshape other than a rectangle, such as a circle or a star.

Although an example of a small battery used in a portable informationterminal or the like is described in this embodiment, one embodiment ofthe present invention is not particularly limited to this example.Application to a large battery provided in a vehicle or the like is alsopossible.

Although an example of application to a lithium-ion secondary battery isdescribed in this embodiment, one embodiment of the present invention isnot limited to this example.

Application to a variety of secondary batteries such as a lead storagebattery, a lithium-ion polymer secondary battery, a nickel-hydrogenstorage battery, a nickel-cadmium storage battery, a nickel-iron storagebattery, a nickel-zinc storage battery, a silver oxide-zinc storagebattery, a solid-state battery, and an air battery is also possible.Application to a variety of power storage devices such as a primarybattery, a capacitor, and a lithium-ion capacitor is also possible.Furthermore, application to a solar cell, an optical sensor, a touchsensor, a display device, a flexible printed circuit (FPC), an opticalfilm (e.g., a polarizing plate, a retardation plate, a prism sheet, alight reflective sheet, and a light diffusion sheet), and the like ispossible.

At least part of this embodiment can be implemented in combination withany of the other embodiments and examples described in thisspecification, as appropriate.

(Embodiment 2)

In this embodiment, examples of electronic devices incorporating abattery obtained using Embodiment 1, in particular, a secondary batterywill be described.

The secondary battery that can be fabricated according to Embodiment 1includes a thin and flexible film as an exterior body and thus canflexibly change its form.

A part of an electronic device like a watch is brought into contact witha part of the body (wrist or arm) of a user, that is, the user wears theelectronic device, whereby the user can feel like the electronic deviceis lighter than the actual weight. A flexible secondary battery can beprovided in an electronic device having a form with a curved surfacethat fits a part of the body of a user so that the secondary battery canbe fixed in a suitable form.

When a user moves a part of the body where an electronic device is on,the user might feel uncomfortable regarding the electronic device as adistraction, and feel stress even in the case where the electronicdevice has a curved surface that fits the part of the body. Anelectronic device provided with a flexible secondary battery in aportion whose form can be changed can change its form at least partlyaccording to movement of the body of a user; thus, an electronic devicewith which the user does not feel uncomfortable can be obtained.

An electronic device does not necessarily have a form with a curvedsurface or a complicated form; an electronic device may have a simpleform. The number or size of components that can be incorporated in anelectronic device with a simple form, for example, is determineddepending on the volume of a space formed by a housing of the electronicdevice in many cases. Providing a flexible secondary battery in a smallspace between components other than the secondary battery enables aspace formed by a housing of an electronic device to be efficientlyused; thus, the electronic device can be reduced in size.

Examples of wearable devices include wearable input terminals such as awearable camera, a wearable microphone, and a wearable sensor; wearableoutput terminals such as a wearable display and a wearable speaker; andwearable input/output terminals having the functions of any of the inputterminals and any of the output terminals. Another example of a wearabledevice is a wearable computer including a CPU, which is a typicalexample of a device that controls each device and calculates orprocesses data. Other examples of wearable devices include devices thatstore data, send data, and receive data, typically, a portableinformation terminal and a memory.

Examples of electronic devices each using a flexible secondary batteryare as follows: display devices such as head-mounted displays and goggletype displays, televisions (also referred to as television receivers),desktop personal computers, laptop personal computers, monitors forcomputers or the like, cameras such as digital cameras or digital videocameras, digital photo frames, electronic notebooks, e-book readers,electronic translators, toys, audio input devices such as microphones,electric shavers, electric toothbrushes, high-frequency heatingappliances such as microwave ovens, electric rice cookers, electricwashing machines, electric vacuum cleaners, water heaters, electricfans, hair dryers, air-conditioning systems such as humidifiers,dehumidifiers, and air conditioners, dishwashers, dish dryers, clothesdryers, futon dryers, electric refrigerators, electric freezers,electric refrigerator-freezers, freezers for preserving DNA,flashlights, electric power tools, alarm devices such as smokedetectors, gas alarm devices, and security alarm devices, industrialrobots, health equipment and medical equipment such as hearing aids,cardiac pacemakers, X-ray equipment, radiation counters, electricmassagers, and dialyzers, mobile phones (also referred to as mobilephone devices or cell phones), portable game machines, portableinformation terminals, lighting devices, headphone stereos, stereos,remote controls, clocks such as table clocks and wall clocks, cordlessphone handsets, transceivers, pedometers, calculators, portable orstationary music reproduction devices such as digital audio players, andlarge game machines such as pachinko machines.

In addition, a flexible secondary battery can be incorporated along acurved inside/outside wall surface of a house or a building or a curvedinterior/exterior surface of an automobile.

FIG. 16A illustrates an example of a mobile phone. A mobile phone 7400includes a display portion 7402 incorporated in a housing 7401, anoperation button 7403, an external connection port 7404, a speaker 7405,a microphone 7406, and the like. Note that the mobile phone 7400includes a secondary battery 7407.

FIG. 16B illustrates the mobile phone 7400 that is bent. When the wholemobile phone 7400 is bent by external force, the secondary battery 7407included in the mobile phone 7400 is also bent. FIG. 16C illustrates thebent secondary battery 7407. The secondary battery 7407 is a laminatedstorage battery (also referred to as a layered battery or a film-coveredbattery). The secondary battery 7407 is fixed while being bent. Notethat the secondary battery 7407 includes a lead electrode 7408electrically connected to a current collector 7409. A film serving as anexterior body of the secondary battery 7407 is embossed, so that thesecondary battery 7407 has high reliability even when bent, for example.The mobile phone 7400 may further be provided with a slot for insertionof a SIM card, a connector portion for connecting a USB device such as aUSB memory.

FIG. 16D illustrates an example of a mobile phone that can be bent. Whenbent to be put around a forearm, the mobile phone can be used as abangle-type mobile phone as in FIG. 16E. A mobile phone 7100 includes ahousing 7101, a display portion 7102, an operation button 7103, and asecondary battery 7104. FIG. 16F illustrates the secondary battery 7104in the state of being bent. When the mobile phone is worn on a user'sarm while the secondary battery 7104 is bent, the housing changes itsform and the curvature of a part or the whole of the secondary battery7104 is changed. Specifically, a part or the whole of the housing or themain surface of the secondary battery 7104 is changed in the range ofradius of curvature from 10 mm to 150 mm inclusive. Note that thesecondary battery 7104 includes a lead electrode 7105 that iselectrically connected to a current collector 7106. Pressing isperformed to form a plurality of projections and depressions on asurface of a film serving as an exterior body of the secondary battery7104, for example; thus, reliability is retained even when the secondarybattery 7104 is bent many times with different curvatures. The mobilephone 7100 may further be provided with a slot for insertion of a SIMcard, a connector portion for connecting a USB device such as a USBmemory. When a center portion of the mobile phone illustrated in FIG.16D is bent, a form illustrated in FIG. 16G can be obtained. When thecenter portion of the mobile phone is folded so that end portions of themobile phone overlap with each other as illustrated in FIG. 16H, themobile phone can be reduced in size so as to be put in, for example, apocket of clothes a user wears. As described above, the mobile phoneillustrated in FIG. 16D can change its form in more than one way, and itis desirable that at least the housing 7101, the display portion 7102,and the secondary battery 7104 have flexibility in order to change theform of the mobile phone.

FIG. 17A illustrates an example of a vacuum cleaner. By being providedwith a secondary battery, the vacuum cleaner can be cordless. To leave adust collecting space for storing vacuumed dust inside the vacuumcleaner, a space occupied by a secondary battery 7604 is preferably assmall as possible. For this reason, it is useful to provide thesecondary battery 7604 that can be bent, between the outside surface andthe dust collecting space.

The vacuum cleaner 7600 is provided with operation buttons 7603 and thesecondary battery 7604. FIG. 17B illustrates the secondary battery 7604in the state of being bent. A film that serves as an exterior body ofthe secondary battery 7604 is embossed, so that the secondary battery7604 has high reliability even when bent. The secondary battery 7604includes a lead electrode 7601 electrically connected to a negativeelectrode and a lead electrode 7602 electrically connected to a positiveelectrode.

As an example of a secondary battery where one current collector isexposed from each short side of an exterior body, a curved secondarybattery 7605 is illustrated in FIG. 17C. In the secondary battery 7605illustrated in FIG. 17C, part of the positive electrode currentcollector 72 is exposed from one short side of the exterior body andpart of the negative electrode current collector 74 is exposed from theother short side of the exterior body. A film serving as the exteriorbody of the secondary battery 7605 is also embossed, so that thesecondary battery 7605 can be bent and has high reliability. Note that astructure in which one lead electrode is exposed from one short side ofan exterior body may be employed.

The thin secondary battery 7604 can be manufactured by the method formanufacturing a laminated secondary battery that is described inEmbodiment 1.

The thin secondary battery 7604 has a laminated structure and is bentand fixed. The vacuum cleaner 7600 includes a display portion 7606 thatdisplays, for example, the remaining amount of power in the thinsecondary battery 7604. A display area of the display portion 7606 iscurved to fit the shape of the outer surface of the vacuum cleaner. Thevacuum cleaner includes a connection cord for being connected to areceptacle. When the thin secondary battery 7604 is charged to havesufficient power, the connection cord can be removed from the receptacleto use the vacuum cleaner. The thin secondary battery 7604 may becharged wirelessly without using the connection cord.

The use of secondary batteries that can be bent in vehicles enablesproduction of next-generation clean energy vehicles such as hybridelectric vehicles (HEVs), electric vehicles (EVs), and plug-in hybridelectric vehicles (PHEVs). Moreover, secondary batteries that can bebent can also be used in moving objects such as agricultural machines,motorized bicycles including motor-assisted bicycles, motorcycles,electric wheelchairs, electric carts, boats or ships, submarines,aircrafts such as fixed-wing aircrafts and rotary-wing aircrafts,rockets, artificial satellites, space probes, planetary probes, andspacecrafts.

FIGS. 18A and 18B each illustrate an example of a vehicle fabricatedusing one embodiment of the present invention. An automobile 8100illustrated in FIG. 18A is an electric vehicle that runs on the power ofan electric motor. Alternatively, the automobile 8100 is a hybridelectric vehicle capable of driving using either an electric motor or anengine as appropriate. In the case of providing a laminated secondarybattery in the vehicle, a battery module including a plurality oflaminated secondary batteries is placed in one place or more than oneplace. One embodiment of the present invention can make a secondarybattery itself compact and lightweight; thus, when the secondary batteryhaving a curved surface is provided on the inside of a tire of avehicle, for example, the vehicle can be a high-mileage vehicle.Furthermore, a secondary battery that can have various shapes can beprovided in a small space in a vehicle, which allows a space in a trunkand a space for riders to be secured. The automobile 8100 includes thesecondary battery. The secondary battery is used not only to drive theelectric motor, but also to supply electric power to a light-emittingdevice such as a headlight 8101 or a room light (not illustrated).

The secondary battery can also supply electric power to a display deviceof a speedometer, a tachometer, or the like included in the automobile8100. Furthermore, the secondary battery can supply electric power to asemiconductor device included in the automobile 8100, such as anavigation system.

FIG. 18B illustrates an automobile 8200. The automobile 8200 can becharged when a secondary battery included in the automobile 8200 issupplied with electric power through external charging equipment by aplug-in system, a contactless power feeding system, or the like. In FIG.18B, a secondary battery included in the automobile 8200 is charged withthe use of a ground-based charging apparatus 8021 through a cable 8022.In charging, a given method such as CHAdeMO (registered trademark) orCombined Charging System may be employed as a charging method, thestandard of a connector, or the like as appropriate. The chargingapparatus 8021 may be a charging station provided in a commerce facilityor a power source in a house. For example, with the use of a plug-intechnique, the secondary battery included in the automobile 8200 can becharged by being supplied with electric power from outside. The chargingcan be performed by converting AC electric power into DC electric powerthrough a converter such as an AC-DC converter.

Furthermore, although not illustrated, the vehicle may include a powerreceiving device so that it can be charged by being supplied withelectric power from an above-ground power transmitting device in acontactless manner. In the case of the contactless power feeding system,by fitting a power transmitting device in a road or an exterior wall,charging can be performed not only when the electric vehicle is stoppedbut also when driven. In addition, the contactless power feeding systemmay be utilized to perform transmission and reception of electric powerbetween two vehicles. Furthermore, a solar cell may be provided in theexterior of the automobile to charge the secondary battery when theautomobile stops or moves. To supply electric power in such acontactless manner, an electromagnetic induction method or a magneticresonance method can be used.

According to one embodiment of the present invention, the degree offlexibility in place where the secondary battery can be provided isincreased; thus, a vehicle can be designed efficiently. Furthermore,according to one embodiment of the present invention, the secondarybattery itself can be made compact and lightweight as a result ofimproved characteristics of the secondary battery. The compact andlightweight secondary battery contributes to a reduction in the weightof a vehicle, and thus increases the driving radius. Furthermore, thesecondary battery included in the vehicle can be used as a power sourcefor supplying electric power to products other than the vehicle. In sucha case, the use of a commercial power source at peak time of electricpower demand can be avoided.

At least part of this embodiment can be implemented in combination withany of the other embodiments and examples described in thisspecification, as appropriate.

EXAMPLE 1

In this example, description will be given of the internal shapes ofbendable batteries (lithium-ion secondary batteries) exemplified inEmbodiment 1 that were fabricated as batteries of one embodiment of thepresent invention and photographed.

Each lithium-ion secondary battery was fabricated by the manufacturingmethod described in Embodiment 1 using LiCoO₂ as a positive electrodeactive material, graphite as a negative electrode active material, andan embossed aluminum laminated film as an exterior body. The thicknessof an electrode stack is approximately 1.5 mm. In the electrode stack,six current collectors each made of aluminum foil and provided with apositive electrode active material layer on one side and six currentcollectors each made of copper foil and provided with a negativeelectrode active material layer on one side are alternately stacked.

As each exterior body, an aluminum laminated film with a thickness ofapproximately 110 μm in which polypropylene, aluminum foil, and nylonare stacked in this order was used. The film was obtained by beingprocessed to have a wave pitch of 2 mm and a height difference between acrest and a trough of 0.5 mm.

Bonding for formation of a bonding portion of the film was performedusing a mold (heat bar) with a flat surface. A pair of bonding layers(side sealing portions) in the direction perpendicular to wave crestlines and wave trough lines were formed by pressure bonding using a heatbar with a width of 1 mm at a pressure of 600 kPa/cm² and a temperatureof 175° C. Meanwhile, a bonding layer (top sealing portion) in thedirection parallel to the wave crest lines and the wave trough lineswere formed by pressure bonding using a heat bar with a width of 2 mmprovided with a groove at the position that faces a lead portion at apressure of 125 kPa/cm² and a temperature of 175° C.

Here, two kinds of samples fabricated as follows were prepared. One ofthe samples, Sample 1, was fabricated in such a manner that a portion ofa film to be a folded portion was planarized and the film was foldedsuch that the phases of waves of portions that overlapped with eachother were different from each other by approximately 180°, that is, thewave crest lines of the portions overlapped with each other and the wavetrough lines of the portions overlapped with each other. Theplanarization was performed on a region with a width of approximately 6mm between the wave crest lines as boundaries by a heat bar press methodat a pressure of 60 kPa/cm² and a temperature of 100° C.

The other sample, Sample 2, was fabricated in such a manner that a filmwas folded such that the phases of waves of facing portions werecoordinate, that is, wave crest lines of one of the portions overlappedwith wave trough lines of the other portion.

The inside of each of the fabricated secondary batteries of the twosamples were observed by X-ray computed tomography (X-ray CT).

FIGS. 19A and 19B are photographs showing the appearance of Sample 1,and FIGS. 19C and 19D are photographs showing the appearance of Sample2. It is found from these photographs that the bonding portion of eachof Sample 1 and Sample 2 was formed to be very flat. In addition, partof the films of each of Sample 1 and Sample 2 was changed in form suchthat the wave period of a portion close to an end portion of the filmwas longer than that of a center portion thereof and the wave amplitudeof the portion close to the end portion of the film was smaller thanthat of the center portion thereof.

FIGS. 20A and 20B are transmission X-ray photographs of Sample 1. FIG.20A is a photograph showing a top surface, and FIG. 20B is a photographshowing a side surface. As shown in FIG. 20A, the folded portion wascurved so as to be more depressed as the distance from the bondingportion (side sealing portion) was larger. In addition, as shown in FIG.20B, a space was formed between the electrode stack and the film.

FIGS. 21A and 21B are transmission X-ray photographs of Sample 2. As inSample 1, the folded portion of Sample 2 was curved so as to be moredepressed as the distance from the bonding portion was larger. It isalso found that a space was formed between the electrode stack and thefilm.

FIG. 22A is an enlarged view of an X-ray CT image of Sample 1 whosefolded portion was observed from the lateral direction. The foldedportion of Sample 1 had a neat arc shape that was substantiallybilaterally symmetric. It is also found from the photograph that thedistance between the electrode stack and the interior wall of the filmwas approximately 2.2 mm in the vicinity of the center of the electrodestack and approximately 2.0 mm in the vicinity of an end portionthereof. As shown in FIG. 22A, the folded portion of the film was formedsuch that wave crest lines were connected; thus, a space in the areasurrounded by the film was formed to be wide in the thickness directionand the end portion of the electrode stack was not in contact with asurface of the film.

FIG. 22B is an enlarged view of an X-ray CT image of Sample 2 whosefolded portion was observed from the lateral direction. The foldedportion of Sample 2 had a distorted shape that was bilaterallyasymmetric. In addition, Sample 2 included not only a portion in whichthe distance between the electrode stack and the interior wall of thefilm was as large as approximately 2.4 mm but also a portion in whichthe distance between the electrode stack and the interior wall of thefilm was as small as approximately 1.3 mm, which demonstrates that anenough space was not formed unlike in Sample 1. Furthermore, as shown inFIG. 22B, one end portion of the electrode stack was partly in contactwith the film, which implies that the one end portion of the electrodestack and the film might rub against each other when the battery isbent.

The above results indicate that the folded portion can be formedsymmetrically in the thickness direction when the phases of waves of thefilm are made to be different from each other by 180°. The above resultsalso show that planarizing a portion of the film to be the foldedportion such that crest lines are connected prevents any wave from beinglocated in a portion where a space is formed, allowing the space to beformed larger also in the thickness direction.

EXAMPLE 2

Results of a tensile test for a film will be described below.

For the test, the film which is the same as that used in Example 1 wasused. The test specimen was a rectangle with a size of 15 mm×100 mm.

In the tensile test, the test specimen was sandwiched by clamps andforce required for tension was measured while the distance between theclamps in the tensile direction was varied. The distance between theclamps before the test specimen was under tension is 50 mm. For thetest, EZ graph (produced by Shimadzu Corporation) was used.

FIG. 23 shows the results of the tensile test. The horizontal axisrepresents the displacement amount of the test specimen, and thevertical axis represents tensile strength. The tensile strength linearlyvaries with a gentle slope until the displacement amount reachesapproximately 4 mm, which shows that the embossed wave shape was changedso as to be stretched. This suggests that the film can be changed inform with weak force. The tensile strength rapidly increases after thedisplacement amount reaches approximately 4 mm, which implies that thetest specimen itself was stretched.

Thus, the use of an embossed layered film that can be easily stretchedfor an exterior body of a battery enables fabrication of the batterythat can be flexibly bent.

EXAMPLE 3

In this example, batteries of one embodiment of the present inventionwere fabricated and influences on the sealing capability of thebatteries by bend tests were examined. Specifically, the amount ofmoisture entry into the film of each of samples subjected to the bendtest and samples not subjected to the bend test was measured.

The batteries used in this example were fabricated by the same method asthat for Sample 1 of Example 1 except for the film bonding temperature.That is, the film of each of the batteries was folded such that wavecrest lines substantially overlap with each other and wave trough linessubstantially overlap with each other. The film bonding for side sealingportions and a top sealing portion was performed at 185° C.

The length of the top sealing portion and the length of the side sealingportions of each of the fabricated batteries are approximately 15 mm and52 mm, respectively. As an electrolytic solution, approximately 400 μLof propylene carbonate (PC) was used.

The measurement of the amount of moisture entry into each of the filmswas performed by the following method. First, an autoclave into whichwater was poured was prepared and the fabricated batteries were put inthe autoclave so as to be immersed. Then, the autoclave was put in athermostat kept at 120° C., and the batteries were boiled forapproximately 25.5 hours. After that, the batteries were taken out, andthe films were each opened in a glove box and 400 μL of PC was added.The added PC and the electrolytic solution in each of the batteries weremixed well to obtain about 0.3 g of the mixture. Then, the amount ofmoisture in the obtained mixture was measured with the Karl Fischermoisture meter (MKC 610 produced by Kyoto Electronics Manufacturing Co.,Ltd.). The amount of moisture entry into each of the films was estimatedby subtracting the amount of moisture originally contained in PC itselffrom the measured amount of moisture.

The following four kinds of batteries were used for the measurement ofthe amount of moisture entry. The first battery is the one not subjectedto the bend test (Condition 1). The second battery is the one repeatedlybent 10000 times with a curvature radius of 40 mm (Condition 2). Thethird battery is the one heated at 160° C. for 15 minutes after beingfabricated (Condition 3). The fourth battery is the one heated at 160°C. for 15 minutes after being fabricated, and repeatedly bent 10000times with a curvature radius of 40 mm (Condition 4).

FIG. 24A shows the measured amount of moisture entry of the batteries ofConditions 1 and 2. The number of measurement samples of Condition 1 is5, and the number of measurement samples of Condition 2 is 7. The amountof moisture entry of the samples of Condition 2 repeatedly bent wassubstantially equal to that of the samples of Condition 1. Thisdemonstrates that repeated bends do not degrade the sealing capabilityof the film. Note that the amount of moisture entry of one of thesamples of Condition 2 was outstandingly larger than that of the restbut was less than 110 ppm, which is low enough to ensure the sealingcapability of the battery.

FIG. 24B shows the measured amount of moisture entry of the batteries ofConditions 3 and 4. The number of measurement samples of Condition 3 is5, and the number of measurement samples of Condition 4 is 3. Themeasurement results of the samples of Condition 3 indicate thatsufficient sealing capability can be ensured even after heating. Themeasurement results of the samples of Condition 4 indicate that repeatedbends after heating do not degrade the sealing capability. Note that thefollowing tendency was observed: the sealing capability of the samplesof Condition 4 was slightly better than that of the samples of Condition3.

The above results demonstrate that the battery of one embodiment hassufficient resistance to repeated bends and a high-temperatureenvironment.

EXAMPLE 4

In this example, batteries were fabricated using exterior bodies withdifferent thicknesses, and force required to bend each of the batterieswas measured.

In this example, batteries (Sample 3, Sample 4, and Sample 5) werefabricated using the following three kinds of exterior bodies. Theexterior body used for each of the samples is an aluminum laminated filmin which polypropylene, aluminum foil, and nylon are stacked. For Sample3, the film with a total thickness of approximately 110 μm in which thethickness of aluminum foil is approximately 40 μm was used. For Sample4, the film with a total thickness of approximately 70 μm in which thethickness of aluminum foil is approximately 30 μm was used. For Sample5, the film with a total thickness of approximately 50 μm in which thethickness of aluminum foil is approximately 20 μm was used.

Note that Samples 3 to 5 were fabricated by the same method as that inExample 3 except for the material of the exterior body.

Next, force required to bend each of the fabricated three samples wasmeasured by the following method. FIGS. 25A and 25B are schematic viewsillustrating the measurement method. A measurement apparatus includes adepressed member on the lower side and a projected member on the upperside. The curvature radius of a curved surface of the depressed memberand the projected member is 30 mm. Each sample was positioned such thatend portions thereof were supported by edge portions of a depressedportion of the depressed member. Then, as illustrated in FIG. 25B, theprojected member was displaced downward while a projected portion of theprojected member was pressed against the sample, whereby the sample inthe state of being flat was curved. Force required to displace theprojected member downward was measured to estimate force required tobend the sample. For the measurement, a compact table-top precisionuniversal tester (EZ-Graph) manufactured by Shimadzu Corporation wasused.

FIG. 26 shows the measurement results. In FIG. 26, the horizontal axisrepresents the displacement amount of the projected member, and thevertical axis represents force required for displacement. An increase inforce required for a bend from a displacement amount of approximately 6mm in FIG. 26 is due to the state where the bottom surface of the samplewas in contact with the top surface of the depressed member and forceapplied so as to press the sample was dominant.

Force required to bend each of the samples was 2N or less when thedisplacement amount was 6 mm or less, which indicates that the batteriesare capable of easily bent.

In addition, as shown in FIG. 26, the following tendency was observed:force required to bend each of the samples increased as the displacementamount increased, that is, the curvature radius of the sample decreased.This is due to the fact that each battery is resilient and force toreturn to the original form increases as the curvature radius decreases.In particular, the film processed to have a wave shape was used as theexterior body; restoring force of the exterior body was presumablydominant.

Comparison between the results of the samples in FIG. 26 shows thatforce required for a bend decreases as the thickness of the exteriorbody decreases. For example, when the displacement amount was 4 mm,force required to bend Sample 3 was approximately twice as strong asthat required to bend Sample 5, and this difference is substantiallyequal to the difference in thickness between Samples 3 and 5. Meanwhile,force required to bend Sample 4 was approximately 1.3 times as strong asthat required to bend Sample 5. Since the thickness of Sample 4 isapproximately 1.4 times that of Sample 5, the difference in forcerequired for bending between Samples 4 and 5 is substantially equal tothe difference in thickness between Samples 4 and 5. These results implythat force required to a bend is proportional to the thickness of thefilm used as the exterior body.

The above results indicate that the battery of one embodiment of thepresent invention requires extremely weak force for a bend owing to theuse of a film having a wave shape as the exterior body, and thatreduction in the thickness of the exterior body enables a bend withweaker force.

EXAMPLE 5

In this example, a watch band incorporating the battery of oneembodiment of the present invention was fabricated.

First, a method for fabricating the band will be described. The band wasfabricated by the following method. The method for fabricating the bandwill be described with reference to FIGS. 27A to 27E.

First, a lower mold and a first upper mold were pressed against amaterial to be molded that was sandwiched therebetween and the materialwas cured with the lower mold and the first upper mold fitting together,so that a lower molded body was formed (FIGS. 27A and 27B). Here, asillustrated in FIG. 27B, a groove was formed in part of the lower moldedbody.

Then, the first upper mold was removed and the battery was placed to befitted in the groove of the lower molded body (FIG. 27C).

After that, a second upper mold and the lower mold were pressed againsta material to be molded that was positioned between the battery and thesecond upper mold and the material was cured with the second upper moldand the lower mold fitting together (FIG. 27D).

After that, the second upper mold and the lower mold were removed, sothat the band incorporating the battery was fabricated (FIG. 27E).

In this example, Sample 6 using a millable silicone raw material as amaterial to be molded and Sample 7 using a liquid silicone raw materialas a material to be molded were fabricated. For Sample 6, a batteryfabricated by a method similar to that for Sample 3 described in Example4 was used, and for Sample 7, a battery fabricated by a method similarto that for Sample 5 described in Example 4 was used.

FIG. 28A is a photograph showing the appearance of the top surface ofSample 6. FIG. 28A shows that the battery was incorporated in amilk-white silicone rubber. FIG. 28B is a photograph showing the statewhere a portion of the band in which the battery was located was bent.

FIGS. 29A and 29B are photographs showing the appearances of the topsurface and a side surface of Sample 7, respectively. The rubber moldedbody of Sample 7 was deeper milk-white than that of Sample 6 but wasslightly transparent, and it was confirmed that the wave shape of theexterior body of the incorporated battery was maintained. FIG. 29C is aphotograph showing the state where a portion of the band in which thebattery was located was bent. The thickness of the film used for theexterior body of Sample 7 was smaller than that of the film used for theexterior body of Sample 6; thus, Sample 7 had higher flexibility and wascapable of being bent with weaker force.

A rubber molded body incorporating the battery of one embodiment of thepresent invention can be fabricated in the aforementioned manner wherean exterior body is covered with rubber and the rubber is molded.Although the shape of a watch band was formed here, one embodiment ofthe present invention is not limited thereto and the battery of oneembodiment of the present invention can be used in any of various rubbermolded bodies.

EXAMPLE 6

In this example, results of bend tests of fabricated batteries of oneembodiment of the present invention will be described.

In this example, the following three kinds of samples, Sample 8, Sample9, and Sample 10 were fabricated.

An aluminum laminated film in which polypropylene, aluminum foil, andnylon are stacked was used as an exterior body of each of Sample 8,Sample 9, and Sample 10. The thickness of aluminum foil is approximately20 μm, and the total thickness of the film is 50 μm. Furthermore, thefilm was processed to have a wave pitch of 2 mm and a height differencebetween a crest surface and a trough surface of 0.5 mm.

Sample 8, Sample 9, and Sample 10 were fabricated by the same method asthat in Example 1 except for how to fold the film.

Sample 8 was obtained by folding the film such that the phases of wavesare different from each other by 180°, that is, the wave crest linesoverlap with each other and the wave trough lines overlap with eachother.

Sample 9 was obtained by folding the film such that the phases of wavesare different from each other, specifically, by approximately 90°.

Sample 10 was obtained by folding the film such that the phases of wavesare coordinate, that is, wave crest lines of one of portions overlapwith wave trough lines of the other portion.

FIGS. 30A, 30B, and 30C are transmission X-ray photographs of Sample 8,Sample 9, and Sample 10, respectively. The photographs show thatalthough the phases of the waves of part of a pair of portions of eachof the films were slightly different because of a film bonding step,desired shapes were substantially obtained.

Subsequently, the bend test was performed on each of Sample 8, Sample 9,and Sample 10. For the test, each sample was repeatedly bent and unbent10000 times with a curvature radius between 40 mm (in bending) and 150mm (in unbending).

FIGS. 31A, 31B, and 31C are photographs showing the appearances of thesamples after the bend tests.

As shown in FIG. 31A, there was no significant change in the appearanceof Sample 8 even after the bend test. As shown by the broken line inFIG. 31B, side sealing portions of Sample 9 were partly changed;however, there was no leakage of an electrolytic solution. In contrast,side sealing portions of Sample 10 were partly significantly distortedas shown by the broken lines in FIG. 31C. In addition, it was foundafter the bend test performed 10000 times that there was leakage of anelectrolytic solution of Sample 10.

The above results show that the side sealing portions of the samples ofthe condition in which the phases of waves of the film are differentfrom each other (Sample 8 and Sample 9) did not easily change theirforms compared with the side sealing portions of the sample of thecondition in which the phases of waves of the film are coordinate(Sample 10). In particular, almost no change in the forms of the sidesealing portions was observed in Sample 8, in which the phases of thewaves of the film are different from each other by 180°, and favorableresults were obtained from Sample 8.

Then, the amount of moisture entry into each of the films of Sample 8and Sample 9 was measured and the sealing capability thereof wasevaluated. The measurement of the amount of moisture entry was performedby a method similar to that in Example 3. Note that leakage of theelectrolytic solution of Sample 10 was observed as described above;thus, Sample 10 was not evaluated. In addition, two Samples 8 fabricatedunder the same conditions and subjected to bend tests and two Samples 9fabricated under the same conditions and subjected to bend tests wereevaluated.

FIG. 32 shows the measured amounts of moisture entry.

The amount of moisture entry of each of Samples 8 was less than 100 ppm,which demonstrates that favorable sealing capability was maintained evenafter bend tests performed 10000 times. Furthermore, Sample 8 includesthe film in which aluminum foil thinner than that of the sample given inExample 3 but the sealing capability of Sample 8 was similar to that ofthe sample given in Example 3.

The amount of moisture entry of each Sample 9 was larger than that ofeach Sample 8. This is presumably because there are portions in which alocal change is easily caused at the position near the side sealingportions as shown in the photograph of the appearance in FIG. 31B, andrepeated changes in form of the portions cause metal fatigue andproduces cracks in the aluminum foil, resulting in degradation ofsealing capability. In particular, the thickness of the aluminum foil ofthis example is much smaller than that of Example 3; thus, a markeddifference in sealing capability may be observed.

Note that the process using an autoclave in water at high temperatureand high pressure that was used in the tests is a check under tougherenvironment conditions than practical conditions, and there was noleakage of the electrolytic solution of Sample 9 due to the bend test.This suggests that practically sufficient sealing capability wasensured.

The above results indicate that even when the samples in which thephases of waves of a film are different from each other are repeatedlybent and unbent, no problems such as leakage of an electrolytic solutionwas caused. In particular, when the phases of waves of the film aredifferent from each other by 180°, sealing capability was hardlydegraded. In other words, when the difference between the phases ofwaves of the film is closer to 180°, resistance to bending and unbendingis higher.

EXAMPLE 7

In this example, calculation results of changes in forms of filmexterior bodies with wave shapes when batteries are bent will bedescribed.

For the calculation, two models (Model1 and Model2) are used. FIGS. 33A1and 33A2 show Model1, and FIGS. 33B1 and 33B2 show Model2. FIGS. 33A1and 33B1 are perspective views of Model1 and Model2, respectively, andFIGS. 33A2 and 33B2 are views of Model1 and Model2 seen from the lateraldirection, respectively.

The calculation models will be described. First, for an exterior body ofeach battery, a structure is assumed in which two films each having awave shape are arranged so as to be spaced and are bonded to each otherin end portions in the width direction. The values of the followingmaterial properties of the films are calculated from the results of thetensile test of the aluminum laminated film obtained in Example 2: theYoung's modulus is assumed to be 4.9×10⁹ Pa; the yield stress is assumedto be 2×10⁷ Pa; the tangent modulus is assumed to be 6.3×10⁷ Pa; and thePoisson's ratio is assumed to be 0.3. For simplification of thecalculation structure, it is assumed that an electrode stack is notprovided in the battery.

The exterior body of the battery of Model1 is a pair of films positionedsuch that the phases of waves are different from each other by 180°, andthe exterior body of the battery of Model2 is a pair of films positionedsuch that the phases of waves are coordinate.

The exterior body of each battery is assumed to change its form along asurface of a rigid body. The rigid body has a surface curved with acurvature radius of 25 mm. Note that part of the rigid body is assumedto have the shape of comb teeth so that the contact condition forcontact portions between crests of the battery and the rigid body is setfor the convenience of the calculation.

A columnar rigid body is placed in the vicinity of an end portion of thebattery, and is displaced in the vertical direction to change the formof the battery as shown by an arrow in FIG. 33A2 and the like.

For the calculation, ANSYS Mechanical APDL 14.0 manufactured by ANSYS,Inc. is used. A mesh condition for the calculation models is as follows:the element type: 285 (three-dimensional four-contact tetrahedronsolid).

There is no noticeable difference between the calculated values ofstress on Model1 and Model2.

FIGS. 34A and 34B each show the shape of Model1 change in form, andFIGS. 35A and 35B each show the shape of Model2 changed in form. FIG.34A and FIG. 35A correspond to FIGS. 33A2 and 33B2, respectively, andFIG. 34B and FIG. 35B correspond to FIGS. 33A2 and 33B2 seen from thereverse side (the back side), respectively.

The shape after a bend will be described. It is found that Model1 ischanged in form uniformly in accordance with the bend, whereas Model2 isnoticeably distorted. Specifically, calculation results of Model1 inFIGS. 34A and 34B each show a symmetric shape. In contrast, calculationresults of Model2 in FIGS. 35A and 35B each show an asymmetric shape. Inparticular, it is observed from the FIG. 35A side that the battery ischanged in form to be twisted such that the front side of the exteriorbody is not in contact with the surface of the rigid body.

Here, as the exterior body of each battery, a pair of films (upper andlower films) is fixed in the side sealing portions. The side sealingportions are located substantially on the neutral plane of the batteryexterior body. Thus, when the battery exterior body is curved, the sidesealing portions do not stretch and the form of a wave-shaped portionbetween the pair of side sealing portions mainly is changed.

When one of the films is bent, it changes its form with a trough lineportion near the neutral plane as a starting point. A crest line portionbetween two trough line portions changes its form in accordance with achange in the forms of two trough line portions on both sides of thecrest line portion. Thus, the pair of films changes its form with thetrough line portions as starting portions. For this reason, a portionbetween two trough line portions proximate to each other with theneutral plane therebetween is presumably most likely to change its form.

In Model1, the difference between the phases of waves is 180° and thusthe distance between two trough line portions proximate to each otherwith the neutral plane therebetween is the shortest; accordingly, Model1is easy to bend.

In addition, in Model1, a straight line connecting two trough lineportions proximate to each other with the neutral plane therebetweenpasses through the center of bending when the battery exterior body isseen from the lateral direction. That is probably why Model1 changes itsform with less distortion as shown in FIGS. 34A and 34B.

In contrast, in Model2, the phases of waves are coordinate and thus thedistance between two trough line portions proximate to each other withthe neutral plane therebetween is the longest; accordingly, Model2 isnot easy to bend.

In addition, in Model2, one trough line portion is proximate to twotrough line portions located on the reverse side with the neutral planebetween the one trough line portion and the two trough line portions.That is, two portions per trough line portion most easily change theirforms. Furthermore, when the battery exterior body is seen from thelateral direction, there are two straight lines connecting one troughline portion and trough line portions proximate to the one trough lineportion, and both the straight lines do not pass through the center ofbending and cross at the one trough line portion. This is a differencefrom Model1. The forms of the two portions per trough line portion thateasily change their forms do not change in the same degree, and the formof one of the portions can change more greatly than the other portion.

Note that which portion easily changes its form is not uniquelydetermined; thus, a portion in which both the forms of the two portionsthat most easily change their forms are greatly changed can be locallygenerated when the battery exterior body is bent. The significantlydistorted portions shown in FIGS. 35A and 35B probably correspond to thetwo portions. This description agrees with the result that the sidesealing portions of Sample 10 in which the phases of the waves arecoordinate were partly significantly distorted because of the bend testas in Example 6.

The above results indicate that the structure of a battery exterior bodywhere the phases of waves are completely coordinate as in Model2 is notsuitable for a bend and the structure where the phases of waves aredifferent from each other is preferred. Furthermore, the structure of abattery exterior body where the phases of waves are different from eachother by 180° as in Model1 is the most preferred.

EXPLANATION OF REFERENCE

-   10: battery, 11: exterior body, 12: stack, 13: electrode, 13 a:    electrode, 13 b: electrode, 21: crest line, 21 a: crest line, 21 b:    crest line, 22: trough line, 22 a: trough line, 22 b: trough line,    25: space, 31: portion, 31 a: portion, 31 b: portion, 32: folded    portion, 33: bonding portion, 34: bonding portion, 41: electrode,    42: electrode, 43: electrode, 50: film, 51: mold, 52: mold, 53:    mold, 54: mold, 55: embossing roll, 55 a: projection, 56: embossing    roll, 56 a: projection, 57: roll, 60: direction, 61: film, 62: film,    63: projection, 64: space, 71: region, 72: positive electrode    current collector, 73: separator, 74: negative electrode current    collector, 75: sealing layer, 76: lead electrode, 77: electrolytic    solution, 78: positive electrode active material layer, 79: negative    electrode active material layer, 80: plane, 90: plane, 7100: mobile    phone, 7101: housing, 7102: display portion, 7103: operation button,    7104: secondary battery, 7105: lead electrode, 7106: current    collector, 7400: mobile phone, 7401: housing, 7402: display portion,    7403: operation button, 7404: external connection port, 7405:    speaker, 7406: microphone, 7407: secondary battery, 7408: lead    electrode, 7409: current collector, 7600: vacuum cleaner, 7601: lead    electrode, 7602: lead electrode, 7603: operation button, 7604:    secondary battery, 7605: secondary battery, 7606: display portion,    8021: charging apparatus, 8022: cable, 8100: automobile, 8101:    headlight, 8200: automobile

This application is based on Japanese Patent Application serial no.2015-210931 filed with Japan Patent Office on Oct. 27, 2015, JapanesePatent Application serial no. 2015-240157 filed with Japan Patent Officeon Dec. 9, 2015, and Japanese Patent Application serial no. 2015-245916filed with Japan Patent Office on Dec. 17, 2015, the entire contents ofwhich are hereby incorporated by reference.

The invention claimed is:
 1. A battery comprising: a stack; and anexterior body, wherein the exterior body has a film-like form and isfolded in half with the stack between facing portions of the exteriorbody, wherein the exterior body includes a pair of first portions, asecond portion, a pair of third portions, and a fourth portion, whereinthe pair of first portions overlaps with each other, wherein each of thefirst portion is surrounded by the second portion, the pair of thirdportions, and the fourth portion and includes a portion overlapping withthe stack, wherein the second portion is a folded portion locatedbetween the pair of first portions, wherein the pair of third portionsis belt-like portions located opposite to each other with each of thefirst portions therebetween and extending in a direction intersectingwith the second portion, wherein the fourth portion is a belt-likeportion located opposite to the second portion with the first portiontherebetween, wherein the exterior body is bonded in the third portionsand the fourth portion, and wherein in an area surrounded by theexterior body, the stack and the second portion are not in contact witheach other but there is a space between the stack and the secondportion.
 2. The battery according to claim 1, wherein in a plan view ofthe exterior body, each of the third portions in an extension directionthereof is longer than a total length of one of the first portions, thesecond portion, and the fourth portion in a direction parallel to theextension direction of the third portions.
 3. The battery according toclaim 1, wherein each of the first portions has a wave shape in which aplurality of crest lines and a plurality of trough lines are parallel toeach other and alternately located, and wherein each of the thirdportions is flat.
 4. The battery according to claim 3, wherein each ofthe first portions includes a region in which a length of a wave periodincreases and a wave amplitude decreases as a distance from the secondportion decreases.
 5. The battery according to claim 3, wherein the pairof first portions of the exterior body includes a region in which thecrest lines of one first portion do not overlap with the trough lines ofthe other first portion.
 6. The battery according to claim 3, whereinthe pair of first portions includes a region in which the crest linesthereof overlap with each other and the trough lines thereof overlapwith each other.
 7. The battery according to claim 3, wherein the secondportion does not have a wave shape.
 8. The battery according to claim 3,wherein one of the crest lines is located between the second portion andthe trough line of the first portion that is located closest to thesecond portion.
 9. The battery according to claim 1, wherein a distancebetween an end portion of the stack on the second portion side and aninterior surface of the exterior body of the battery in the state ofbeing unbent is greater than or equal to π×t when a thickness of thestack is 2t.
 10. The battery according to claim 9, wherein there is adistance between the end portion of the stack on the second portion sideand the interior surface of the exterior body when the battery is bent180°.
 11. The battery according to claim 3, wherein a boundary of thesecond portion coincides with the crest line of the wave shape of thepair of the first portions.
 12. A battery comprising: a stack; and anexterior body, wherein the exterior body has a film-like form and isfolded in half with the stack between facing portions of the exteriorbody, wherein the exterior body includes a pair of first portions and asecond portion, wherein the pair of first portions overlaps with eachother, wherein each of the first portions includes a portion overlappingwith the stack, wherein the second portion is a folded portion locatedbetween the pair of first portions, wherein in an area surrounded by theexterior body, the stack and the second portion are not in contact witheach other but there is a space between the stack and the secondportion, wherein each of the first portions has a wave shape in which aplurality of crest lines and a plurality of trough lines are parallel toeach other and alternately located, and wherein the pair of firstportions of the exterior body includes a region in which the crest linesof one first portion do not overlap with the trough lines of the otherfirst portion.
 13. The battery according to claim 12, wherein each ofthe first portions includes a region in which a length of a wave periodincreases and a wave amplitude decreases as a distance from the secondportion decreases.
 14. The battery according to claim 12, wherein thepair of first portions includes a region in which the crest linesthereof overlap with each other and the trough lines thereof overlapwith each other.
 15. The battery according to claim 12, wherein one ofthe crest lines is located between the second portion and the troughline of the first portion that is located closest to the second portion.16. The battery according to claim 12, wherein a distance between an endportion of the stack on the second portion side and an interior surfaceof the exterior body of the battery in the state of being unbent isgreater than or equal to π×t when a thickness of the stack is 2t.